Semiconductor device

ABSTRACT

A semiconductor device having a display unit, which is small in size, suppresses the defect caused by the mounting of IC chips and the like on the substrate, and operates at a high speed. A semiconductor display unit and other circuit blocks are integrally formed on the substrate having an insulating surface by using a process for fabricating TFTs that realize a high degree of mobility. Concretely, there is employed a process for crystallizing a semiconductor active layer by using a continuously oscillating laser. Further, the process for crystallization relying upon the continuously oscillating laser is selectively effected for only those circuit blocks that must be operated at high speeds, thereby to realize a high production efficiency.

BACKGROUND OF THE INVENTION

1. Filed of the Invention

The present invention relates to a semiconductor device having a displayportion. In particular, the present invention relates to a semiconductordevice in which thin film transistors are formed over a substrate havingan insulation film surface thereon.

2. Related Art of the Invention

Semiconductor devices and, particularly, electronic devices having asemiconductor display unit have been vigorously developed in recentyears, and their applications can be represented by such portabledevices as game devices, notebook PCs, cellular phones as well as suchdiversities as liquid crystal TVs, liquid crystal displays, EL displaysand so on. As compared to the traditional CRTs, the semiconductordisplay units can be realized in reduced weights, reduced thickness andconsuming electric power in small amounts.

As the conventional semiconductor display units, there have been known asemiconductor display unit of the passive matrix type having a pixelregion on which striped electrodes are formed in a manner to intersecteach other on the upper and lower sides with the liquid crystal layer orlight-emitting layer sandwiched therebetween, and a semiconductordisplay unit of the active matrix type having a pixel region on whichthin-film transistors (TFTs) are arranged like a matrix.

In recent years, technology has advanced for forming TFTs over asubstrate, and efforts have been made to apply the semiconductor displayunit of the active matrix type. In particular, the TFTs using apolysilicon film exhibit an electric field effect mobility (often calledsimply as mobility) which is higher than that of the conventional TFTsusing an amorphous silicon film, and are making it possible to controlthe pixels by a drive circuit formed over the same substrate as that ofthe pixels though the pixels have heretofore been controlled by a drivecircuit outside the substrate.

Next, the constitution of an electronic device having a conventionalsemiconductor display unit will be described. FIG. 21 is a block diagramschematically illustrating portions related to the display of an image.In FIG. 21, a semiconductor device 301 receives or forms image data,processes the image data, converts the format, and displays the image.Examples of the semiconductor device 301 include game devices, videocameras, car navigation systems, personal computers and so on.

On the semiconductor device 301, a semiconductor display unit 302 isconstituted by a pixel region 319, a scanning line drive circuit 318 anda signal line drive circuit 317, and is formed as a unitary structure ona substrate having an insulating surface. Other circuit blocks areformed on different silicon substrates and are mounted in the form of ICchips. Some of the circuit blocks may often be formed over the samesilicon substrate.

The semiconductor device 301 is constituted by an input terminal 311, afirst control circuit 312, a second control circuit 313, a CPU 314, afirst memory 315, a second memory 316, and the semiconductor displayunit 302. The input terminal 311 receives data that serve as the basisof image data depending upon the kind of the electronic devices. Forexample, the input data are those through an antenna in the case of abroadcast receiver, and the input data are those from a CCD in the caseof a video camera. The input data may be those from a DV tape or amemory card. The data input through the input terminal 311 are convertedinto image signals through the first control circuit 312. The firstcontrol circuit 312 processes the image signals, such as decoding theimage data that are compressed and encoded according to the MPEGstandard and the tape format, and interpolating and resizing the image.The image signals output from the first control circuit 312 and theimage signals formed or processed by the CPU 314, are fed to the secondcontrol circuit 313, and are converted into a format (e.g., scanningformat, etc.) that is adapted to the semiconductor display unit 302. Thesecond control circuit 313 produces image signals and control signals ofwhich the formats have been converted.

The CPU 314 efficiently controls the signal processing in the firstcontrol circuit 312, second control circuit 313 and other interfacecircuits. The CPU 314 further forms and processes the image data. Thefirst memory 315 is used as a memory region for storing image data fromthe first control circuit 312 and for storing image data from the secondcontrol circuit 313, as a work memory region for executing the controloperation by using a CPU, and as a work memory region at the time offorming the image data by the CPU. As the first memory 315, there can beused a DRAM or an SRAM. The second memory 316 stores the color data andcharacter data, and is necessary when the image data are to be formed orprocessed by the CPU 314. The second memory 316 is constituted by a maskROM or an EPROM.

The semiconductor display unit 302 is constituted by the signal linedrive circuit 317, scanning line drive circuit 318 and pixel region 319.The signal line drive circuit 317 receives image signals and controlsignals from the second control circuit 313 (clock signals, start pulsesignals and the like), and the scanning line drive circuit 318 receivescontrol signals (clock signals, start pulse signals and the like) fromthe second control circuit 313. The pixel region 319 displays the image.

The electronic device having the semiconductor display unit can assume avariety of constitutions in addition to the constitution shown in FIG.21. The simplest constitution may comprise the semiconductor displayunit, input/output terminals and a simple control circuit as exemplifiedby a liquid crystal display or an EL display. When the CPU bears a toolarge load in the architecture shown in FIG. 21, an image processor maybe newly provided to reduce the burden of the CPU.

In the conventional electronic device having the semiconductor displayunit described above, the circuit blocks other than the drive circuitare mounted being formed over a substrate separate from the substrateover which the pixels are formed.

Accompanying the widespread use of portable electronic devices, it isbecoming an important assignment to realize the electronic devices insmall sizes. The thus constituted semiconductor devices, however,require many IC chips that are mounted over the substrates separate fromthe substrate over which the pixels are formed, and involve difficultyif they are to be realized in small sizes. In particular, even if thecircuit blocks are realized in small sizes in the IC chip, a largemargin required for the mounting makes it difficult to fabricate theentire device in a small size. If it is attempted to decrease the marginfor the mounting to realize the device in a small size, then, a highdegree of mounting technology is needed arousing a problem from thestandpoint of cost and reliability in the mounting portion. Therefurther remains the problem of wiring capacity. That is, when the ICchips are mounted, the wiring must bear a large load making it difficultto conduct the operation at high speeds.

As a method of solving these problems, it has been expected to form thecircuit blocks integrally with the semiconductor display unit.

When the circuit blocks are formed over the substrate having aninsulating surface, however, a problem often arouses concerning theoperation speed. This is because, the TFTs formed over the substratesuch as a glass surface having an insulating surface exhibit propertiessuch as mobility and threshold values which are inferior to those of thetransistors formed over a single crystalline silicon substrate.

When the conventional semiconductor devices are operated at a givenfrequency, therefore, a desired operation is realized when the circuitblocks are mounted in the form of IC chips but the desired operation isnot realized when the circuit blocks are formed over the substratehaving the insulating surface.

SUMMARY OF THE INVENTION

This invention was accomplished in view of such problems. It is anassignment of this invention to provide an electronic device having asemiconductor display unit which can be realized in a small size, whichdecreases defects that accompanies the mounting of IC chips over thesubstrate and which operates at high speeds.

In order to solve the above assignment according to this invention, thesemiconductor display unit and other circuit blocks are integrallyformed over the substrate having an insulating surface.

Further, a TFT fabrication process for realizing a high degree ofmobility is employed in order to lessen the problem of operation speedwhen the circuit blocks are formed over the substrate having aninsulating surface.

According to the TFT fabrication process for realizing a high degree ofmobility, a semiconductor film is irradiated with an energy beam to forma molten band which is continuously scanned in the channel direction tocrystallize the molten band so as to form an active layer. Concretelyspeaking, this process is carried out by using a continuous wave laseralthough the details will be described later in Examples.

The circuit blocks constituted by the thus fabricated TFTs make itpossible to greatly increase the operation frequency since theindividual TFTs exhibit a high degree of mobility as compared to that ofthe circuit blocks that use the conventional polysilicon as the TFTactivating layer.

As a result, it is allowed to integrally form the display unit and othercircuit blocks over the substrate having the insulating surface therebyto realize a high-speed operation. Namely, this invention now makes itpossible to put into practical use even those circuit blocks which, sofar, could not be placed in practice despite they were formed over thesubstrate having the insulating surface due to the problem related tothe operation speed.

Besides, this invention improves the throughput in a manner as describedbelow while maintaining such a high operation frequency.

A YVO₄ laser, a YLF laser and a YAG laser have been known as continuouswave lasers. However, their outputs are as small as about 10 watts evenat the greatest. To crystallize the active layer by the irradiation witha continuous wave laser beam, therefore, the laser beam must be sharplyfocused to have a beam width of about 50 to about 500 μm (typically 200μm).

When, for example, the whole surface of a glass substrate measuring 600mm×720 mm is scanned with a laser beam at a scanning speed of 50 cm/sec,a time of 72 minutes is required per a piece. In practice, further,longer time is needed due to shifting of the scanning direction of thelaser beam and acceleration. Namely, the technology encounters theproblem of a low throughput.

This invention has a feature in that the crystallization process basedon the continuous wave laser is selectively carried out for only thecircuit blocks that need a high-speed operation. This greatly improvesthe throughput of the crystallization process by using the continuouslyoscillating laser.

By suppressing the region irradiated with the continuous wave laser beamto be, for example, not larger than 50% (preferably, not larger than30%) of the substrate area, the time required for the crystallizationprocess by using the continuous wave laser can be decreased down toabout 50% (preferably, not longer than 30%).

It is further desired to arrange the circuit blocks that need high-speedoperation in the regions as close to each other as possible in order tosuppress the moving distance of the continuously oscillating laser beamor of the substrate. This further helps improve the throughput of thecrystallization process by using the continuous wave laser.

In order to further improve the operation frequency of the circuitblock, it is desired to bring the direction of channel length of theTFTs into agreement with the scanning direction of the laser beam. Thisis because, in the process for crystallizing the semiconductor film byusing the continuous wave laser, the highest degree of mobility isobtained when the channel direction of the TFTs is nearly in parallel(desirably, from −30° to 30°) with the scanning direction of the laserbeam for the substrate. The TFTs formed by the crystallizing process byusing the continuous wave laser comprises active layers formed by apolycrystalline semiconductor in which crystalline grains extends in thechannel direction. This means that crystalline grain boundaries areformed along the channel direction. Therefore, the electric character ofthe active layers is different between the channel direction and thedirection perpendicular to the channel direction. In a word, the activelayers crystallized by using the continuous wave laser has an electricanisotropy in the channel direction.

The semiconductor active layer included in the circuit block or in thepixel region which needs not be crystallized by the continuous wavelaser, may be formed by a known method of formation.

In particular, it is desired to apply a crystallization process thatoffers a higher throughput than that of the crystallization process thatuses the continuous wave laser.

It is particularly desired to employ a method of crystallizing thesemiconductor film (thermal crystallization by using a metal catalyst)disclosed in Japanese Patent Laid-Open No. 7-183540. In this case, inthe region where the semiconductor film is crystallized by thecontinuous wave laser, a process is carried out by combining the thermalcrystallization using a metal catalyst with the crystallization using acontinuous wave laser. Here, as demonstrated in Examples, the aboveprocess forms the TFTs having a mobility equal to, or greater than, thatin the crystallization conducted by using the continuous wave laseronly.

A method of crystallization by laser by using a pulse oscillation lasermay be employed for the semiconductor active layer in the region wherethe crystallization based on the continuous wave laser is not carriedout. The pulse oscillation laser produces a large output, being capableof emitting a beam of a width of not smaller than 100 mm, and offers ahigh throughput. From the standpoint of operation frequency and cost,the person who carries out the process may employ known methods offorming the active layer in free combination. The TFTs formed by a knownmanufacturing method are different from the TFTs formed by thecrystallization process by using the continuous wave laser.Specifically, the shape of crystal grains in active layers of the TFTsformed by a known method have no anisotropy in the channel direction, orhave an anisotropy in the channel direction which is weaker than that ofthe TFTs formed by the crystallization process by using the continuouswave laser. In addition, the active layers of the TFTs formed by a knownmethod have no electric anisotropy in the channel direction, or have anelectric anisotropy in a channel direction which is weaker than that ofthe TFTs formed by the crystallization process by using the continuouswave laser.

In this invention as described above, the pixel region and the circuitblocks are formed over the same substrate, the process forcrystallization by using the continuous wave laser is selectivelyeffected for only those circuit blocks that need a high-speed operation,to provide a semiconductor device which lowers the occurrence of defectthat stems from a reduction in the size and from the mounting of ICchips over the substrate, and which realizes a high-frequency operationand a high throughput. The high-speed operation can be realized evenfrom the standpoint of wiring capacity.

The semiconductor device referred to in this invention stands fordevices that work by utilizing the semiconductor characteristics, ingeneral, such as semiconductor display devices as represented by aliquid crystal display device and a light-emitting device, andelectronic devices having a semiconductor display unit. Thesemiconductor display unit stands for the one obtained by formingelectrodes or thin-film transistors over a substrate having aninsulating surface, such as a liquid crystal display unit, alight-emitting display unit, a display unit of the passive matrix typeand a display unit of the active matrix type. When it is apparent, thesemiconductor display unit is also simply referred to as display unit.

Further, the circuit block referred to in this invention stands for ablock of an electric circuit exhibiting functions of characteristicsconstituted by such circuit elements as transistors, capacitor elementsor resistor elements, and includes a signal line drive circuit, ascanning line drive circuit, a register, a decoder, a counter, afrequency-divider circuit, a memory, a CPU, and a DSP. In thisspecification, in particular, the circuit block is formed over thesubstrate having an insulating surface and, hence, the thin-filmtransistors (hereinafter referred to as TFTs) play the role of principalconstituent elements in the circuit blocks. Here, the thin-filmtransistors (TFTs) stand for the transistors as a whole that are formedby using the SOI technology.

The configuration of the present invention is shown as below.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by irradiating a semiconductor filmwith an energy beam to form a molten band and by continuously scanningthe molten band in the direction of channel length so as to becrystallized, and the second active layer being formed by crystallizingthe semiconductor film by the treatment with heat, wherein: the pixelregion is constituted by the second TFTs; the scanning line drivecircuit is constituted by the second TFTs; and the signal line drivecircuit is constituted by the first TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by irradiating a semiconductor filmwith an energy beam to form a molten band and by continuously scanningthe molten band in the direction of channel length so as to becrystallized, and the second active layer being formed by adding a metalelement to the semiconductor film and crystallizing the semiconductorfilm by the treatment with heat, wherein: the pixel region isconstituted by the second TFTs; the scanning line drive circuit isconstituted by the second TFTs; and the signal line drive circuit isconstituted by the first TFTs.

The foregoing energy beam may be a continuously oscillating laser beam.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by irradiating a semiconductor filmwith an energy beam to form a molten band and by continuously scanningthe molten band in the direction of channel length so as to becrystallized, and the second active layer being formed by irradiatingthe semiconductor film with a pulse-like energy beam so as to becrystallized, wherein: the pixel region is constituted by the secondTFTs; the scanning line drive circuit is constituted by the second TFTs;and the signal line drive circuit is constituted by the first TFTs.

The foregoing energy beam comprises pulses of an oscillating laser beam.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorin which the crystalline grains are extending in the channel direction,and the second active layer being formed by a polycrystallinesemiconductor in which the polycrystalline grains have no shapeanisotropy in the channel direction, wherein: the pixel region isconstituted by the second TFTs; the scanning line drive circuit isconstituted by the second TFTs; and the signal line drive circuit isconstituted by the first TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning fine drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorin which the crystalline grains are extending in the channel direction,and the second active layer being formed by a polycrystallinesemiconductor in which the polycrystalline grains have a shapeanisotropy in the channel direction which is weaker than that of thefirst active layer, wherein: the pixel region is constituted by thesecond TFTs; the scanning line drive circuit is constituted by thesecond TFTs; and the signal line drive circuit is constituted by thefirst TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorhaving an electric anisotropy in the channel direction, and the secondactive layer being formed by a polycrystalline semiconductor withouthaving electric anisotropy in the channel direction, wherein: the pixelregion is constituted by the second TFTs; the scanning line drivecircuit is constituted by the second TFTs; and the signal line drivecircuit is constituted by the first TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorhaving an electric anisotropy in the channel direction, and the secondactive layer being formed by a polycrystalline semiconductor having anelectric anisotropy in the channel direction which is weaker than thatof the first active layer, wherein: the pixel region is constituted bythe second TFTs; the scanning line drive circuit is constituted by thesecond TFTs; and the signal line drive circuit is constituted by thefirst TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorin which the crystalline grains are extending in the channel directionand have a grain size of from 0.5 to 100 μm in the direction of shortdiameter thereof and a particle size of from 3 to 10,000 μm in thedirection of long diameter thereof, and the second active layer beingformed by a polycrystalline semiconductor in which the crystallinegrains have a grain size of from 0.01 μm to 10 μm, wherein: the pixelregion is constituted by the second TFTs; the scanning line drivecircuit is constituted by the second TFTs; and the signal line drivecircuit is constituted by the first TFTs.

It is preferable that the drive frequency of the scanning line drivecircuit is from 1 kHz to 1 MHz, and the drive frequency of the signalline drive circuit is from 100 kHz to 100 MHz.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by irradiating a semiconductor filmwith an energy beam to form a molten band and by continuously scanningthe molten band in the direction of channel length so as to becrystallized, and the second active layer being formed by treating thesemiconductor film with heat so as to be crystallized, wherein: thepixel region is constituted by the second TFTs; the scanning line drivecircuit is constituted by the first TFTs; and the signal line drivecircuit is constituted by the first TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by irradiating a semiconductor filmwith an energy beam to form a molten band and by continuously scanningthe molten band in the direction of channel length so as to becrystallized, and the second active layer being formed by adding a metalelement to the semiconductor film and crystallizing the semiconductorfilm by the treatment with heat, wherein: the pixel region isconstituted by the second TFTs; the scanning line drive circuit isconstituted by the first TFTs; and the signal line drive circuit isconstituted by the first TFTs.

The energy beam may be a continuous wave laser beam.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by irradiating a semiconductor filmwith an energy beam to form a molten band and by continuously scanningthe molten band in the direction of channel length so as to becrystallized, and the second active layer being formed by irradiatingthe semiconductor film with a pulse-like energy beam so as to becrystallized, wherein: the pixel region is constituted by the secondTFTs; the scanning line drive circuit is constituted by the first TFTs;and the signal line drive circuit is constituted by the first TFTs.

The energy beam comprises pulses of an oscillating laser beam.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorin which the crystalline grains are extending in the channel direction,and the second active layer being formed by a polycrystallinesemiconductor in which the polycrystalline grains have no anisotropy inthe channel direction, wherein: the pixel region is constituted by thesecond TFTs; the scanning line drive circuit is constituted by the firstTFTs; and the signal line drive circuit is constituted by the firstTFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorin which the crystalline grains are extending in the channel direction,and the second active layer being formed by a polycrystallinesemiconductor in which the polycrystalline grains have a shapeanisotropy in the channel direction which is weaker than that of thefirst active layer, wherein: the pixel region is constituted by thesecond TFTs; the scanning line drive circuit is constituted by the firstTFTs; and the signal line drive circuit is constituted by the firstTFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorhaving an electric anisotropy in the channel direction, and the secondactive layer being formed by a polycrystalline semiconductor withouthaving electric anisotropy in the channel direction, wherein: the pixelregion is constituted by the second TFTs; the scanning line drivecircuit is constituted by the first TFTs; and the signal line drivecircuit is constituted by the first TFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorhaving an electric anisotropy in the channel direction, and the secondactive layer being formed by a polycrystalline semiconductor having anelectric anisotropy in the channel direction weaker than that of thefirst active layer, wherein: the pixel region is constituted by thesecond TFTs; the scanning line drive circuit is constituted by the firstTFTs; and the signal line drive circuit is constituted by the firstTFTs.

In accordance with the invention, a semiconductor device is offered, inwhich a pixel region, a scanning line drive circuit and a signal linedrive circuit are provided over the same substrate, and has first TFTswith a first active layer and second TFTs with a second active layer,the first active layer being formed by a polycrystalline semiconductorin which the crystalline particles are extending in the channeldirection and have a grain size of from 0.5 to 100 μm in the directionof short diameter thereof and a particle size of from 3 to 10,000 μm inthe direction of long diameter thereof, and the second active layerbeing formed by a polycrystalline semiconductor in which the crystallinegrains have a particle size of from 0.01 μm to 10 μm, wherein: the pixelregion is constituted by the second TFTs; the scanning line drivecircuit is constituted by the first TFTs; and the signal line drivecircuit is constituted by the first TFTs.

It is desired that the drive frequency of the scanning line drivecircuit is from 10 kHz to 1 MHz, and the drive frequency of the signalline drive circuit is from 100 kHz to 100 MHz.

In the semiconductor device, the memory may be provided over the samesubstrate as that of the pixel regions, the memory being constituted bythe first TFTs.

The memory may be an SRAM having a read cycle time of not longer than200 nsec.

The memory is a DRAM having a read cycle time of not longer than 1 μsec.

The CPU may be provided over the same substrate as that of the pixelregions, the CPU being constituted by the first TFTs.

It is preferred that the operation frequency of the CPU is not lowerthan 5 MHz.

The image processing circuit may be provided over the same substrate asthat of the pixel regions, the image processing circuit beingconstituted by the first TFTs.

It is preferred that the operation frequency of the image processingcircuit is not lower than 5 MHz.

The DSP is provided over the same substrate as that of the pixelregions, the DSP being constituted by the first TFTs.

It is preferred that the operation frequency of the image processingcircuit is not lower than 5 MHz.

The timing generating circuit is provided over the same substrate asthat of the pixel regions, the timing generating circuit beingconstituted by the first TFTs.

It is preferred that the substrate is any one of a plastic substrate, aglass substrate and a quartz substrate.

It is preferred that the area of the circuits constituted by the firstTFT's is not larger than 50% of the area of the substrate.

It is preferred that the circuits constituted by the first TFTs areformed in 1 to 10 rectangular regions, the areas of the rectangularregions not being larger than 50% of the area of the substrate.

The semiconductor device may be a liquid crystal display device.

The semiconductor device may be a light-emitting device.

The semiconductor device may be any one selected from a game device, avideo camera, a head-mounted type display, a DVD player, a personalcomputer, a cell phone and a car audio device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a semiconductor device of this invention viewed fromthe top;

FIG. 2 is a view of the semiconductor device of this invention viewedfrom the top;

FIGS. 3A-3D are sectional views illustrating the steps of manufacturingTFTs for constituting the semiconductor device of this invention;

FIGS. 4A-4D are sectional views illustrating the steps of manufacturingTFTs for constituting the semiconductor device of this invention;

FIGS. 5A-5D are sectional views illustrating the steps of manufacturingTFTs for constituting the semiconductor device of this invention;

FIG. 6 is a view schematically illustrating an optical system used forirradiating a laser beam;

FIG. 7 is a photograph of a SEM image on the surface of a crystallinesemiconductor film;

FIG. 8 is a photograph of a SEM image on the surface of a crystallinesemiconductor film;

FIG. 9 is a diagram of Raman scattering spectra of semiconductor films;

FIGS. 10A-10H are sectional views illustrating the steps ofmanufacturing TFTs;

FIGS. 11A and 11B are graphs illustrating electric characteristics ofTFTs;

FIGS. 12A-12C are sectional views illustrating the steps ofcrystallizing the semiconductor;

FIGS. 13A and 13B are graphs illustrating electric characteristics ofTFTs;

FIGS. 14A and 14B are graphs illustrating electric characteristics ofTFTs;

FIGS. 15A and 15B are graphs illustrating electric characteristics ofTFTs;

FIG. 16 is a block diagram illustrating the semiconductor device of thisinvention;

FIG. 17 is a block diagram illustrating the semiconductor device of thisinvention;

FIG. 18 is a block diagram illustrating the semiconductor device of thisinvention;

FIGS. 19A-19G are views illustrating electronic devices using thesemiconductor display unit of the invention;

FIG. 20 is a view illustrating a method of irradiating a laser beam;

FIG. 21 is a block diagram illustrating a conventional semiconductordevice; and

FIG. 22 is a view of a semiconductor device of this invention viewedfrom the top.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

A semiconductor display device of the active matrix type will now bedescribed as a representative example of the semiconductor device havinga display unit of the invention.

FIG. 2 is a view illustrating the constitution of the semiconductordisplay device of the active matrix type of the invention viewed fromthe top. In FIG. 2, the semiconductor display device of the activematrix type is constituted by a pixel region 202, a scanning line drivecircuit 204, a signal line drive circuit 203, a wiring 205, and an FPC206 formed over a substrate 201.

The operation of the semiconductor display device of the active matrixtype will now be briefly described.

The signal line drive circuit 203 receives image signals, clock signalsand a start pulse, and the scanning line drive circuit 204 receivesclock signals and a start pulse, from an external unit through the FPC206, respectively. The pixel region 202 displays an image.

In the pixel region, a plurality of signal lines and a plurality ofscanning lines are so arranged as to intersect one another, and thepixel TFTs are arranged at the points where the signal lines intersectthe scanning lines. A scanning line is connected to the gate electrodeof the pixel TFT, a signal line is connected to either the sourceelectrode or the drain electrode, and a liquid crystal element isconnected to the remaining one of either the source electrode or thedrain electrode.

The display operation of the pixel will now be described. When thescanning line is selected, the pixel TFT connected to the selectedscanning line is turned on. When a data is input to the signal lineconnected to the pixel TFT, a potential of the signal line is applied toa liquid crystal element, and the liquid crystal element changes itslight transmission factor depending upon an applied voltage. Thus, theluminance of the pixel is determined to make a display.

An image is formed as the scanning lines are all selected successively.While the scanning lines are being selected, further, the data is inputto all of the signal lines successively or at one time, and the imagedata is input to a selected row. A period in which one image isdisplayed is called one frame. It is desired that not less than 60frames are displayed in a second.

According to the above operation method, a driving frequency necessaryfor a driving circuit is roughly determined if the number of pixels isdetermined. Under the color VGA standard, for example, the number ofpixels is 640×480×RGB. If the operation is presumed to be 60frames/second, a period for selecting one scanning line is aboutTg=1/60/480 sec=35 μsec. Further, if receiving the image data ispresumed to be RGB×1 pixel per a clock, then, each clock must be roughlyTd=Tg/640 sec=54 nsec. The time for inputting the data to the pixelbecomes roughly a period (Tg=35 μsec) for selecting one scanning linewhen the lines are successively driven.

The real operation frequency varies depending upon the number ofdividing the image data, frame frequency, and fly-back period. It isrequired that the pixel and scanning line drive circuits operate at afrequency of 1 to 100 kHz, and the signal line drive circuit operates ata frequency of 0.1 to 100 MHz.

In the foregoing was described the case of the liquid crystal displaydevice. The display devices having a light-emitting layer as representedby the EL layer share a common system in that an image is formed as thescanning lines are all selected successively and that the data is inputsuccessively or at one time to all of the signal lines during a periodin which the scanning lines are being selected, and the image data isinput to the selected raw, though the driving methods may differ to someextent. Therefore, the same idea can be applied to the drivingfrequency, too.

Based upon the above consideration of operation frequency, theembodiment 1 deals with a case where a process for fabricatinghigh-mobility TFTs is applied to the region that includes the signalline drive circuit 203 that must be operated at a high speed. Namely, inFIG. 2, a method of crystallizing the semiconductor film by thecontinuously oscillating laser is applied to the first region 207 only.A known technology for forming the active layer may be used for theregions other than the first region.

In FIG. 2, the first region 207 can be reduced to be not larger than 30%(preferably, not larger than 10%) of the substrate 201, and the timerequired for the continuously oscillating laser process can be shortenedto be roughly not more than 30% (preferably, not more than 10%) of thetime required for processing by using the continuously oscillating laserwith respect to the whole substrate.

In the embodiment 1, a process for fabricating high mobility TFTs isemployed for the first region 207 that includes the signal line drivecircuit which determines the speed, to realize a semiconductor displaydevice of the active matrix type achieving a high-speed operation as awhole. Further, a high throughput is realized despite of using acrystallization process using the continuously oscillating laser.

Though the embodiment 1 has applied the process for fabricatinghigh-mobility TFTs to the region including the signal line drivecircuit, the above process can be further applied to the region thatincludes the scanning line drive circuit or may be applied to the regionthat includes pixels. In particular, even when the process forfabricating high-mobility TFTs is applied to the region that includesall of TFTs, the throughput increases as compared to a case that theprocess is applied to the whole substrate.

Embodiment 2

A semiconductor device having a display unit will now be described as arepresentative example of the semiconductor device having the displayunit of the invention.

FIG. 1 is a view illustrating the constitution of the semiconductordevice having the display unit of the invention viewed from the top. InFIG. 1, the semiconductor device having the display unit is constitutedby a semiconductor display unit 102, a first control circuit 112, asecond control circuit 113, a CPU 114, a first memory 115, a secondmemory 116, and an input/output terminal 111 formed over a substrate101. Further, the semiconductor display unit 102 is constituted by apixel region 119, a signal line drive circuit 117 and a scanning linedrive circuit 118.

The semiconductor device shown in FIG. 1 receives or forms image data,processes the image data, converts the format and displays the image.The block constitution is the same as that of the block diagram of FIG.21. The operation and function are as illustrated in FIG. 21, and arenot described here.

The operation frequencies of the circuit blocks vary depending upon theindividual semiconductor devices, and cannot be definitely stated.Usually, however, other circuit blocks operate in synchronism with theoperation frequency of the CPU. It is therefore desired to improve theoperation frequencies of the CPU 114 and the circuit blocks connected tothe bus.

In the embodiment 2, therefore, the process for fabricatinghigh-mobility TFTs is applied to the CPU 114, the first control circuit112, the second control circuit 113, the first memory 115 and the secondmemory 116 that are connected to the bus, as well as to the signal linedrive circuit 117. Namely, in FIG. 1, the method of crystallizing thesemiconductor active layer based on the continuous wave laser is appliedonly to the first region 103. A known technology for forming the activelayer may be used for the regions other than the first region.

In FIG. 1, the first region 103 can be reduced to be not larger than 50%(preferably, not larger than 30%) of the substrate, and the timerequired for the process with the continuous wave laser can be shortenedto be not more than about 50% (preferably, not more than 30%) of thetime required for processing with the continuous wave laser with respectto the whole substrate.

It is further desired that the region where the semiconductor activelayer is crystallized by using the continuous wave laser isconcentratedly located as much as possible from the standpoint ofthroughput. In the constitution shown in FIG. 1, it is possible toreplace the positions of the signal line drive circuit and the scanningline drive circuit by each other. By arranging the signal line drivecircuit that must be operated at a high speed near the CPU 114 and thefirst control circuit 112, second control circuit 113, first memory 115and second memory 116 that are connected to the bus, the first region isconcentratedly located on the substrate.

Owing to this arrangement, the position of irradiation with thecontinuous wave laser beam needs not be moved to the whole surface ofthe substrate, and the time required for the crystallization can beshortened as compared to the case that the continuous wave laser isirradiated onto a plurality of regions having the same area scatteredover the substrate.

It is thus desired that the areas for being irradiated with thecontinuous wave laser beam are concentratedly located on the substrate.It is therefore desired that the continuous wave laser or the substratemoves in a simple manner and that the regions for being irradiated withthe continuous wave laser beam are reduced to several (preferably, oneto ten) regions as represented by rectangles.

In the embodiment 2, the semiconductor device for accomplishing ahigh-speed operation of the device as a whole is realized by using theprocess for fabricating high-mobility TFTs in the first region 103 whichincludes a system having the CPU 114 that must be operated at highspeeds. By reducing the ratio of the first region to the substrate,further, a high throughput is realized despite of using the process forcrystallization based on the continuous wave laser.

In the embodiment 2, the process for fabricating the high-mobility TFTsis applied to the region that includes the CPU 114, first controlcircuit 112, second control circuit 113, first memory 115, second memory116 and signal line drive circuit 117. Even when operated at the samefrequency, however, characteristics required for the TFTs differdepending upon the constitutions of the circuit blocks.

For example, when particularly high degree of characteristics arerequired for the TFTs that constitute the CPU 114, first control circuit112 and first memory 115, the process for fabricating high-mobility TFTscan be applied to only regions that include the above circuits.

In such a case, too, it is desired to contrive the arrangement of theCPU 114, first control circuit 112 and first memory 115 so that theactive layer is crystallized with the continuous wave laser in a shortperiod of time.

It is allowable to apply the process for fabricating high-mobility TFTsto the region that includes the scanning line drive circuit or theregion that includes pixels, in addition to the first region, as amatter of course. Even when the process for fabricating high-mobilityTFTs is applied to all of the regions that include the TFTs, thethroughput is improved as compared to the case where the process forfabricating high-mobility TFTs is applied to the whole substrate.

In this embodiment, although the circuit blocks have been roughlydivided like the CPU and the memory, the invention is not limitedthereto. Smaller circuit constitutions such as a register, a frequencydivider circuit, may be used as circuit blocks. The process forcrystallization based on the continuous wave laser may be selectivelyapplied to such small blocks.

When the crystallization process using a continuous wave laser isapplied to large circuit blocks such as the CPU and the memory, theprocess needs not necessarily be applied to the entire surfaces thereof.The process can further be selectively applied to only regions ofrelatively high operation frequencies in the circuit blocks.

Working examples of the invention will now be described.

EXAMPLE 1

In this example, a method for performing a laser beam irradiation to anyregion over the substrate is described with reference to FIGS. 6 and 20.

FIG. 6 shows a view schematically illustrating a device used for forminga linear beam and irradiating a laser beam to a substrate.

A laser beam emitted from a laser 601 is incident into a convex lens 603via a mirror 602. Here, as the laser 601, anyone of a solid state laser,a gas laser and a metal laser of continuous oscillation or pulseoscillation may be used. However, used in this example is YAG laser ofcontinuous wave. Then, a laser oscillated from the laser 601, may beconverted into a higher harmonic wave by a non-linear optical element.Moreover, a beam expander between the laser 601 and the mirror 602 orbetween the mirror 602 and the convex lens 603 is set and may beexpanded into the desired size in both of longer direction and shorterdirection, respectively. The beam expander is particularly effective inthe case where the shape of the laser beam emitted from the laser issmall. Moreover, the mirror may not be set, or a plurality of themirrors may be set.

The laser beam is made slantly incident with respect to the convex lens603. The focal position is shifted with aberration such as astigmatismby being incident in such a way, a linear beam 606 can be formed on theirradiation surface or in its neighborhood. It should be noted that ifthe convex lens 603 is made of a synthetic quartz glass, it is desiredsince a high transparency is obtained. Moreover, as for the convex lens,it is desirable that an aspherical lens whose spherical lens aberrationis corrected is used. If an aspherical lens is used, the condensingproperty is enhanced, and the aspect ratio and the distribution of theenergy density are also enhanced.

In addition, the “linear shape” described here means not a “line” in thestrict sense but a rectangle (or a prolate ellipsoid shape) having ahigh aspect ratio. For example, it indicates a shape having an aspectratio of 2 or more (preferably, 10 to 10000). Note that the linear shapeis used to obtain an energy density required for sufficiently annealingan object to be irradiated. In addition, the linear beam has nonecessity to be a linear shape in the strict sense.

Then, while the linear beam 606 formed thus irradiates, for example, itcan irradiate the desired region or whole area on the irradiated body604 by being relatively moved with respect to the irradiated body 604,for example, in the direction indicated with the reference numeral 607or the directions indicated with the reference numeral 608. “To berelatively moved” is concretely referred to “to operate the irradiatedbody disposed on the stage”.

Then, while the linear beam formed thus irradiates, for example, it canirradiate the desired region or whole area on the irradiated body 604 bybeing relatively moved with respect to the irradiated body 604, forexample, in the direction indicated with the reference numeral 607 orthe directions indicated with the reference numeral 608. “To berelatively moved” is concretely referred to “to operate the irradiatedbody disposed on the stage”. The state of irradiating the laser beam tothe substrate is shown in FIG. 20. An arrow illustrated over a laserirradiation region 609 illustrates the track of the irradiating laser.

In addition, the optical system for generating laser may be other knownones.

EXAMPLE 2

In this example, a method for crystallizing a semiconductor film byusing a continuous wave laser used to a process for manufacturing a TFTwith high mobility in a semiconductor device of the invention isdescribed.

As a base film, a silicon oxynitride film (composition ratio: Si=32%,O=59%, N=7%, and H=2%) in 400 nm thick is formed over a glass substrateby plasma CVD method. Then, as a semiconductor film, 150 nm of amorphoussilicon film is formed on the base film by plasma CVD method. Then,thermal processing at 500° C. is performed thereon for three hours sothat hydrogen contained in the semiconductor film is discharged. Afterthat, the semiconductor film is crystallized by laser annealing method.

As the laser used for laser annealing method, continuous wave YVO₄ laseris used. For the laser annealing method, the second harmonic (wavelength532 nm) of the YVO₄ laser is used as laser light. As the beam in apredetermined form, laser light is irradiated to the semiconductor filmformed on the substrate surface by using an optical system.

As an optical system used when laser light is irradiated to asemiconductor film over a substrate surface, used is an optical systemdescribed in Example 1 (refer to FIG. 6).

In Example 2, the elliptical beam of 200 μm×50 μm is formed havingincident angle φ of about 20° of laser light with respect to the convexlens. The elliptical beam is irradiated on the glass substrate 105 bybeing moved at the speed of 50 cm/s. Thus, the semiconductor film iscrystallized.

The relative scanning direction of the elliptical beam is perpendicularto the major axis of the elliptical beam.

The seco etching is performed on the crystalline semiconductor filmobtained in this way. FIG. 7 shows the result of the observation of thesurface by using an SEM with 10,000 magnifications. The seco solutionused for the seco etching is manufactured by adding K₂Cr₂O₇ as additiveto HF:H₂O=2:1. One shown in FIG. 7 is obtained by relatively scanninglaser light in a direction indicated by an arrow shown in FIG. 7. Largecrystal grains are formed in parallel with the scanning direction of thelaser light. In other words, the crystal is raised so as to extend inthe scanning direction of the laser light.

In this way, large crystal grains are formed on the crystallizedsemiconductor film by using the method according to this example.Therefore, when the semiconductor film is used as a semiconductor activelayer to manufacture a TFT, the number of the crystal grain boundariesincluded in the channel forming area of the TFT can be reduced. Inaddition, each crystal grain internally has crystallinity, which isessentially single crystal. Therefore, the mobility (field effectmobility) as high as that of a transistor using a single crystalsemiconductor can be obtained.

Furthermore, when the TFT is positioned such that the direction that thecarrier moves can be the same as the direction that the formed crystalgrains extend, the number of times that the carriers cross the crystalgrain boundary can be extremely reduced. Therefore, a variation in ONcurrent value (value of drain current flowing when the TFT is ON), anOFF current value (value of drain current flowing when the TFT is OFF),a threshold voltage, an S-value and field effect mobility can bereduced. As a result, the electric characteristic can be improvedsignificantly.

In order to irradiate the elliptical beam 606 in a wide range of thesemiconductor film, the elliptical beam 606 is scanned in a directionperpendicular to the major axis to irradiate to the semiconductor filmmultiple times. Here, the position of the elliptical beam 606 is shiftedin the direction parallel to the major axis for every single scan. Thescanning direction becomes opposite between serial scans. In the serialtwo scans, one will be called outward scan and the other will be calledinward scan hereinafter.

The amount of shifting the position of the elliptical beam 606 to thedirection parallel to the major axis for every single scan is expressedby pitch d. A reference numeral D1 indicates, in the outward scan, thelength of the elliptical beam 606 in the direction perpendicular to thescanning direction of the elliptical beam 606 in an area having largecrystal grains as shown in FIG. 7. A reference numeral D2 indicates, inthe inward scan, the length of the elliptical beam 606 in the directionperpendicular to the scanning direction of the elliptical beam 606 in anarea having large crystal grains as shown in FIG. 11. In this case, anaverage value of D1 and D2 is D.

Here, an overlap ratio R_(O.L) [%] is defined by Equation 1.R _(O.L)=(1−d/D)×100  [EQ1]

In this example, the overlap ratio R_(O.L) is 0%.

EXAMPLE 3

Example 3 shows another example of a method for crystallizing asemiconductor film by using a continuous wave laser used to a processfor manufacturing a TFT with high mobility in a semiconductor device ofthe present invention that is different from Example 2.

The steps up to forming an amorphous silicon film as a semiconductorfilm are the same as those of the Example 2. After that, the methoddisclosed in Japanese Patent Application Laid-open No. 7-183540 is used.Nickel acetate solution (5 ppm in weight conversion concentration and 10ml in volume) is coated on the semiconductor film by spin coatingmethod. Then, thermal processing is performed thereon in a nitrogenatmosphere at 500° C. for one hour and in a nitrogen atmosphere at 550°C. for twelve hours. Then, the crystallinity of the semiconductor filmis improved by laser annealing method.

As the laser used for laser annealing method, continuous wave YVO₄ laseris used. For the laser annealing method, the second harmonic (wavelength532 nm) of the YVO₄ laser is used as laser light. The elliptical beam of200 μm×50 μm is formed having incident angle φ of about 20° of laserlight with respect to the convex lens 103 in the optical system shown inFIG. 6. The elliptical beam is moved and irradiated to the glasssubstrate 105 at the speed of 50 cm/s. Thus, the crystallinity of thesemiconductor film is improved.

The relative scanning direction of the elliptical beam 606 isperpendicular to the major axis of the elliptical beam 606.

The seco etching is performed on the crystalline semiconductor filmobtained in this way. FIG. 8 shows the result of the observation of thesurface by using an SEM with 10,000 magnifications. One shown in FIG. 8is obtained by relatively scanning laser light in a direction indicatedby an arrow shown in FIG. 8. Large crystal grains extend in the scanningdirection.

In this way, large crystal grains are formed in the crystallizedsemiconductor film according to the present invention. Therefore, whenthe semiconductor film is used to manufacture a TFT, the number of thecrystal grain boundaries included in the channel forming region of theTFT can be reduced. In addition, each crystal grain internally hascrystallinity, which is essentially single crystal. Therefore, themobility (field effect mobility) as high as that of a transistor using asingle crystal semiconductor can be obtained.

Furthermore, the formed crystal grains are aligned in one direction.Thus, when the TFT is positioned such that the direction that thecarriers move can be the same as the direction that the formed crystalgrains extend, the number of times that the carriers cross the crystalgrain boundary can be extremely reduced. Therefore, a variation in ONcurrent value, an OFF current value, a threshold voltage, an S-value andfield effect mobility can be reduced. As a result, the electriccharacteristic can be improved significantly.

In order to irradiate the elliptical beam 606 in a wide range of thesemiconductor film, the elliptical beam 606 is scanned in a directionperpendicular to the major axis to irradiate to the semiconductor filmmultiple times (this operation may be called scan). Here, the positionof the elliptical beam 606 is shifted in the direction parallel to themajor axis for every single scan. The scanning direction becomesopposite between continuous scans. In the continuous two scans, one willbe called outward scan and the other will be called inward scanhereinafter.

The amount of shifting the position of the elliptical beam 606 to thedirection parallel to the major axis for every single scan is expressedby pitch d. A reference numeral D1 indicates, in the outward scan, thelength of the elliptical beam 606 in the direction perpendicular to thescanning direction of the elliptical beam 606 in an area having largecrystal grains as shown in FIG. 8. A reference numeral D2 indicates, inthe inward scan, the length of the elliptical beam 606 in the directionperpendicular to the scanning direction of the elliptical beam 606 in anarea having large crystal grains as shown in FIG. 8. In this case, anaverage value of D1 and D2 is D.

Here, an overlap ratio R_(O.L) [%] is defined like Equation 1. In thisexample, the overlap ratio R_(O.L) is 0%.

In FIG. 9, a thick line indicates a result of Raman spectroscopyperformed on the crystalline semiconductor film (represented by ImprovedCG-Silicon in FIG. 9) obtained by using the above-describedcrystallization method. Here, for comparison, a thin line indicates aresult of Raman spectroscopy performed on the single crystal silicon(represented by ref. (100) Si Wafer in FIG. 9). In FIG. 9, a dotted lineindicates a result of Raman spectroscopy performed on a semiconductorfilm (represented by excimer laser annealing in FIG. 9). In order toobtain the semiconductor film, an amorphous silicon film is formed andhydrogen contained in the semiconductor film is discharged throughthermal processing. Then, the semiconductor film is crystallized byusing excimer laser with pulse oscillation.

The Raman shift of the semiconductor film obtained by using the methodof this example has the peak at 517.3 cm⁻¹. The half value breadth is4.96 cm⁻¹. On the other hand, the Raman shift of the single crystalsilicon has the peak at 520.7 cm⁻¹. The half value breadth is 4.44 cm⁻¹.The Raman shift of the semiconductor film crystallized by using theexcimer laser with the pulse oscillation has the peak at 516.3 cm⁻¹. Thehalf value breadth is 6.16 cm⁻¹.

From the results in FIG. 9, the crystallinity of the semiconductor filmobtained by using the crystallization method described in this exampleis closer to that of the single crystal silicon than the crystallinityof the semiconductor film crystallized by using the excimer laser withpulse oscillation.

EXAMPLE 4

In this example, a case where a semiconductor film crystallized by usingthe method described in the Example 2 is used to manufacture a TFT willbe described with reference to FIGS. 6, 10 and 11.

A glass substrate is used as a substrate 20 in this example. As a basefilm 21, 50 nm of silicon oxynitride film (composition ratio Si=32%,O=27%, N=24%, and H=17%) and 100 nm of silicon oxynitride film(composition ratio Si=32%, O=59%, N=7%, and H=2%) are stacked on theglass substrate by plasma CVD method. Next, as a semiconductor film 22,150 nm of amorphous silicon film is formed on the base film 21 by plasmaCVD method. Then, thermal processing is performed thereon at 500° C. forthree hours to discharge hydrogen contained in the semiconductor film(FIG. 10A).

After that, the second harmonic (wavelength 532 nm, 5.5 W) of thecontinuous oscillating YVO₄ laser is used as the laser light to form anelliptical beam of 200 μm×50 μm having incident angle φ of about 20° oflaser light with respect to the convex lens 603 in the optical systemshown in FIG. 6. The elliptical beam is irradiated on the semiconductorfilm 202 by relatively being scanned at the speed of 50 cm/s (FIG. 10B).

Then, first doping processing is performed thereon. This is channeldoping for controlling the threshold value. B₂H₆ is used as material gashaving a gas flow amount of 30 sccm, a current density of 0.05 μA, anaccelerating voltage of 60 keV, and a dosage of 1×10¹⁴/cm² (FIG. 10C).

Next, after etching the semiconductor film 24 into a desired form bypatterning, a silicon oxynitride film in 115 nm thick is formed byplasma CVD method as a gate insulating film 27 covering the etchedsemiconductor film. Then, a TaN film 28 in 30 nm thick and a W film 29in 370 nm thick are stacked on the gate insulating film 27 as aconductive film (FIG. 10D).

A mask (not shown) made of resist is formed thereon by usingphotolithography method, and the W film, the TaN film and the gateinsulating film are etched.

Then, the mask made of resist is removed, and a new mask 33 is formed.The second doping processing is performed thereon and an impurityelement imparting the n-type to the semiconductor film is introduced. Inthis case, the conductive layers 30 and 31 are masks for the impurityelement imparting the n-type, and an impurity region 34 is formed in aself-aligned manner. In this example, the second doping processing isperformed under two conditions because the semiconductor film is thickas much as 150 nm. In this example, phosfin (PH₃) is used as materialgas. The dosage of 2×10¹³/cm² and the accelerating voltage of 90 keV areused, and then the dosage of 5×10¹⁴/cm² and the accelerating voltage of10 keV are used for the processing (FIG. 10E).

Next, the mask 33 made of resist is removed, and a new mask 35 made ofresist is formed additionally for performing the third dopingprocessing. Through the third doping processing, an impurity region 36is formed containing an impurity element for imparting the oppositeconductive type against the one conductive type to the semiconductorfilm which is an active layer of a p-channel TFT. By using theconductive layers 30 and 31 as a mask for the impurity element, theimpurity region 36 is formed in the self-aligned manner by addition ofthe impurity element for imparting the p-type. Also the third dopingprocessing in this example is performed under two conditions because thesemiconductor film is thick as much as 150 nm. In this example, diborane(B₂H₆) is used as material gas. The dosage of 2×10¹³/cm² and theaccelerating voltage of 90 keV are used, and then the dose amount of1×10¹⁵/cm² and the accelerating voltage of 10 keV are used for theprocessing (FIG. 10F).

Through these steps, the impurity regions 34 and 36 are formed in therespective semiconductor layers.

Next, the mask 35 made of resist is removed, and silicon oxynitride film(composition ratio Si=32.8%, O=63.7%, and N=3.5%) in 50 nm thick isformed as a first interlayer insulating film 37 by plasma CVD method.

Next, thermal processing is performed thereon to recover crystallinityof the semiconductor layers and to activate the impurity elements addedto the semiconductor layers, respectively. Then, thermal processing bythermal annealing method using an anneal furnace is performed at 550° C.for four hours in a nitrogen atmosphere (FIG. 10G).

Next, a second interlayer insulating film 38 of an inorganic or organicinsulating material is formed on the first interlayer insulating film37. In this example, after forming a silicon nitride film in 50 nm thickby CVD method, a silicon oxide film in 400 nm thick is formed.

After the thermal processing, hydrogenation processing can be performed.In this example, the thermal processing is performed at 410° C. for onehour in a nitrogen atmosphere by using an anneal furnace.

Next, a wiring 39 is formed for connecting to the impurity regionselectrically. In this example, the wiring 39 is formed by patterning alaminate film of a Ti film in 50 nm thick, an Al—Si film in 500 nm thickand a Ti film in 50 nm thick. Naturally, the construction is not limitedto the two-layer construction, but may be a single layer construction ora laminate construction having three or more layers. The material of thewiring is not limited to Al and Ti. For example, Al and/or Cu may beformed on a TaN film. Then, a laminate film having a Ti film may bepatterned to form a wiring FIG. 10H).

In this way, the n-channel TFT 51 and the p-channel TFT 52 are formed,both having the channel length of 6 μm and the channel width of 4 μm.

FIGS. 11A and 11B show results of measuring these electricalcharacteristics. FIG. 11A shows an electric characteristic of then-channel TFT 51. FIG. 11B shows an electric characteristic of thep-channel TFT 52. The electric characteristics are measured at twomeasurement points in a range of gate voltage Vg=−16 to 16 V and in therange of drain voltage Vd=1 V and 5 V. In FIGS. 11A and 11B, the draincurrent (ID) and the gate current (IG) are indicated by solid lines. Themobility (μFE) is indicated by a dotted line.

Because large crystal grains are formed in the semiconductor filmcrystallized according to the above-described method, the number ofcrystal grain boundaries containing the channel forming region can bereduced when a TF1 is manufactured by using the semiconductor film.Furthermore, because the formed crystal grains direct to the samedirection, the number of times of crossing the crystal grain boundariesby carriers can be extremely reduced. Therefore, a TFT having the goodelectric characteristic can be obtained as shown in FIGS. 11A and 11B.Especially, the mobility is 524 cm²/Vs in the n-channel TFT and 205cm²/Vs in the p-channel TFT.

The method for activating the semiconductor film by using a continuouswave laser shown in this example is applicable to the TFT constituting acircuit block that needs high-speed operation. In particular, when thechannel direction of the TFT is nearly in parallel (desirably, from −30°to 30°) with the scanning direction of the laser beam for the substrate,the operational characteristic of the circuit block virtually identicalto that of a circuit block formed on a monocrystal silicon substrate canbe obtained.

EXAMPLE 5

In this example, a case where a TFT is manufactured by using asemiconductor film crystallized by using the method described in Example3 will be described with reference to FIGS. 6, 12, 14 and 15.

The steps up to forming the amorphous silicon film as the semiconductorfilm are the same as Example 4. The amorphous silicon film is formed in150 nm thick (FIG. 12A).

After that, the method disclosed in the Japanese Patent ApplicationLaid-Open No. Hei 7-183540 is used. Nickel acetate solution (5 ppm inweight conversion concentration and 10 ml in volume) is coated on thesemiconductor film by spin coating method to form a metal containinglayer 41. Then, thermal processing is performed thereon in a nitrogenatmosphere at 500° C. for one hour and in a nitrogen atmosphere at 550°C. for twelve hours. Then, a semiconductor film 42 is obtained (FIG.12B).

Then, the crystallinity of the semiconductor film 42 is improved bylaser annealing method.

As the laser used for laser annealing method, continuous wave YVO₄ laseris used. For the condition for the laser annealing method, the secondharmonic (wavelength 532 nm, 5.5 W) of the YVO₄ laser is used as laserlight. The elliptical beam of 200 μm×50 μm is formed having incidentangle φ of about 20° of laser light with respect to the convex lens 603in the optical system shown in FIG. 6. The elliptical beam is moved andirradiated to the substrate at the speed of 20 cm/s or 50 cm/s. Thus,the crystallinity of the semiconductor film 42 is improved. As a result,a semiconductor film 43 is obtained (FIG. 12C).

The steps after the crystallizing the semiconductor film in FIG. 12C arethe same as the steps shown in FIGS. 10C to 10H shown in Example 5. Inthis way, the n-channel TFT 51 and the p-channel TFT 52 are formed, bothhaving the channel length of 6 μm and the channel width of 4 μm. Theseelectrical characteristics are measured.

FIGS. 13A to 15B show electric characteristics of the TFT manufacturedthrough these steps.

FIGS. 13A and 13B show these electrical characteristics of a TFTmanufactured by moving the substrate at the speed of 20 cm/s in thelaser annealing step in FIG. 12C. FIG. 13A shows an electriccharacteristic of the n-channel TFT 51. FIG. 13B shows an electriccharacteristic of the p-channel TFT 52. FIGS. 14A and 14B show theseelectrical characteristics of a TFT manufactured by moving the substrateat the speed of 50 cm/s in the laser annealing step in FIG. 12C. FIG.14A shows an electric characteristic of the n-channel TFT 51. FIG. 14Bshows an electric characteristic of the p-channel TFT 52.

The electric characteristics are measured in a range of gate voltageVg=−16 to 16 V and in the range of drain voltage Vd=1 V and 5 V. InFIGS. 13A to 14B, the drain current (ID) and the gate current (IG) areindicated by solid lines. The mobility (μFE) is indicated by a dottedline.

Because large crystal grains are formed in the semiconductor filmcrystallized according to the present invention, the number of crystalgrain boundaries contained in the channel forming region can be reducedwhen a TFT is manufactured by using the semiconductor film. Furthermore,the formed crystal grains direct to the same direction. In addition, thesmall number of grain boundaries is laid in a direction crossing therelative scanning direction of laser light. Therefore, the number oftimes of crossing the crystal grain boundaries by carriers can beextremely reduced.

Accordingly, a TFT having the good electric characteristic can beobtained as shown in FIGS. 13A to 14B. Especially, the mobility is 510cm²/Vs in the n-channel is TFT and 200 cm²/Vs in the p-channel TFT inFIGS. 13A and 14B. The mobility is 595 cm²/Vs in the n-channel TFT and199 cm²/Vs in the p-channel TFT in FIGS. 14A and 14B. When asemiconductor apparatus is manufactured by using this type of TFT, theoperational characteristic and the reliability can be also improved.

FIGS. 15A and 15B show these electrical characteristics of a TFTmanufactured by moving the substrate at the speed of 50 cm/s in thelaser annealing step in FIG. 12C. FIG. 15A shows an electriccharacteristic of the n-channel TFT 51. FIG. 15B shows an electriccharacteristic of the p-channel TFT 52.

The electric characteristics are measured in a range of gate voltageVg=−16 to 16 V and in the range of drain voltage Vd=0.1 V and 5 V.

As shown in FIGS. 15A and 15B, a TFT having the good electriccharacteristic can be obtained. Especially, the mobility is 657 cm²/Vsin the n-channel TFT in FIG. 15A and 219 cm²/Vs in the p-channel TFT inFIG. 15B. When a semiconductor apparatus is manufactured by using thistype of TFT, the operational characteristic and the reliability can bealso improved.

The method for activating the semiconductor film by using a continuouswave laser shown in this example is applicable to the TFT constituting acircuit block that need high-speed operation. In particular, when thechannel direction of the TFT is nearly in parallel (desirably, within30°) with the scanning direction of the laser beam for the substrate,the operational characteristic of the circuit block virtually identicalto that of a circuit block formed over a monocrystal silicon substratecan be obtained.

EXAMPLE 6

In this example, the manufacturing steps of a semiconductor device inwhich a plurality of circuits and an active matrix liquid displayportion are integrated over one substrate will be described withreference to FIGS. 3A and 4D.

Cross-sectional views shown in FIGS. 3A and 4D comprise a first region,a second region and a third region.

The first region is a circuit block that particularly requireshigh-speed operation (for example, a CPU, a signal driver circuit andthe like), in which a method for crystallizing a semiconductor film byusing continuous wave laser is performed in the invention. Further, thesecond region denotes circuit blocks other than that of the first region(for example, a scanning driver circuit), while the third region denotesa pixel region.

In addition, an n-channel TFT and a p-channel TFT representing a circuitblock and an n-channel TFT (a pixel TFT) and a storage capacitorrepresenting a pixel region are shown in FIGS. 3A to 4D.

A quartz substrate, a silicon substrate, or a metal or stainlesssubstrate formed with an insulating film on its surface is used as asubstrate 5000. Further, a plastic substrate having heat-resistance,which can withstand a process temperature in the manufacturing process,may also be used. In this example, there is used the substrate 5000 madeof glass such as barium borosilicate glass or alumino borosilicateglass.

Next, a base film 5001 comprised of an insulating film such as a siliconoxide film, a silicon nitride film, or a silicon oxynitride film isformed on the substrate 5000. The base film 5001 in this example takes atwo-layer structure. However, there may be adopted a single layerstructure of the insulating film or a structure in which two or morelayers of the insulating film are laminated.

In this example, as the first layer of the base film 5001, a siliconoxynitride film 5001 a is formed from SiH₄, NH₃, and N₂O as a reactiongas to have a thickness of 10 to 200 nm (preferably 50 to 100 nm) byplasma CVD method. In this example, the silicon oxynitride film 5001 ais formed with a thickness of 50 nm. Then, as the second layer of thebase film 5001, a silicon oxynitride film 5001 b is formed from SiH₄ andN₂O as a reaction gas to have a thickness of 50 to 200 nm (preferably100 to 150 nm) by plasma CVD method. In this example, the siliconoxynitride film 5001 b is formed with a thickness of 100 nm.

Subsequently, semiconductor layers 5002 to 5005, 6002 and 6003 areformed on the base film 5001. As to the semiconductor layers 5002 to5005, 6002 and 6003, a semiconductor film is formed with a thickness of25 to 80 nm (preferably 30 to 60 nm) by known means (sputtering method,LPCVD method, plasma CVD method, or the like). Note that an amorphoussemiconductor film, a microcrystalline semiconductor film, a crystallinesemiconductor film, a compound semiconductor film with an amorphousstructure such as an amorphous silicon germanium film, or the like maybe used as the semiconductor film.

Next, a first crystallization is performed to the second and the thirdregions, or throughout the substrate of the semiconductor film. As afirst crystallization method, known crystallization methods (lasercrystallization method, thermal crystallization method using RTA orfurnace annealing, thermal crystallization method using a metal elementthat promotes crystallization, or the like) may be used.

In this example, a 55-nm-thick amorphous silicon film is formed by usingplasma CVD method. Then, as the first crystallization method, a solutioncontaining nickel is applied onto the amorphous silicon film,dehydrogenation (500° C., 1 hour) is performed to the amorphous siliconfilm, and then, thermal crystallization (550° C., 4 hours) is conductedthereto, thereby forming a crystalline silicon film.

Note that in case that the first crystalline semiconductor film isformed by the laser crystallization method, the crystallization can beperformed to only the second and third regions, or throughout thesubstrate of the semiconductor film. As the laser, used may be a pulseoscillation type gas laser or solid laser. As the former gas laser, anexcimer laser, YAG laser, YVO₄ laser, YLF laser, YAlO₃ laser, glasslaser, ruby laser, Ti:sapphire laser, or the like may be used. Also, asthe latter solid laser, there may be used a laser which uses crystalssuch as YAG, YVO4, YLF, or YAlO₃ which is doped with Cr, Nd, Er, Ho, Ce,Co, Ti or Tm. A fundamental wave of the laser concerned differsdepending on the material to be doped, and the laser light having afundamental wave of about 1 μm is obtained. A harmonic wave with respectto the fundamental wave can be obtained by using a non-linear opticalelement.

The crystallization conditions are appropriately set. However, in thecase of using an excimer laser, it is preferable that the pulseoscillation frequency is 300 Hz and the laser energy density is 100 to700 mJ/cm² (typically 200 to 300 mJ/cm²). Further, in the case of usinga YAG laser, it is preferable that the pulse oscillation frequency is 1to 300 Hz and the laser energy density is 300 to 1000 mJ/cm² (typically350 to 500 mJ/cm²) by using the second harmonic wave. The laser lightcondensed into a linear shape with a width of 100 to 1000 μm (preferablywidth of 400 μm) is irradiated to the entire surface of the substrate.The overlap ratio of the linear beam at this time may be 50 to 98%.

Subsequently, a second crystallization is performed to the semiconductorfilm of the first region. A continuous wave laser is used for a secondcrystallization method. The methods for crystallization by using acontinuous wave laser shown in Examples 2 and 3 can be adopted. Thus, asecond crystalline silicon is obtained.

Through these semiconductor crystallization processes, the firstcrystalline silicon film is formed in the first region including thecircuit block that requires high-speed operation, and the secondcrystalline silicon formed in other regions, respectively.

Since large crystal grains extend in the relative scanning direction ofthe laser beam in the first crystalline silicon film, the TFT in whichthe first crystalline silicon film functions as an active layer has goodelectric characteristic.

In particular, when the channel direction is nearly in parallel to thescanning direction of the laser beam, the number of times that thecarriers cross the crystal grain boundary can be extremely reduced, theelectric characteristic identical to that of TFTs formed on amonocrystal silicon can be obtained.

On the other hand, since continuous wave laser has a narrow beamwidth(50 to 500 um), using such a crystallization process to a wide regionhas a disadvantage from the viewpoint of throughput. In the invention,the crystallization using continuous wave laser is confined to a limitedregion over the substrate to improve the throughput.

Subsequently, the semiconductor layers 5002 to 5005, 6002 and 6003 areformed by a patterning process using a photolithography method.

However, in this example, since the crystallization of the amorphoussilicon film is conducted by using the metal element that promotescrystallization, the metal element remains in the crystalline siliconfilm. Therefore, an amorphous silicon film with a thickness of 50 to 100nm is formed over the crystalline silicon film, and heat treatment(thermal annealing using RTA or furnace annealing, or the like) isperformed thereto to diffuse the metal element into the amorphoussilicon film. After the heat treatment, the amorphous silicon film isremoved by conducting etching. As a result, the metal element in thecrystalline silicon film can be reduced in content or removed.

Note that, after the semiconductor layers 5002 to 5005, 6002 and 6003are formed, doping of a minute amount of impurity element (boron orphosphorus) may be conducted for controlling the threshold value of theTFT.

Subsequently, a gate insulating film 5006 is formed which covers thesemiconductor layers 5002 to 5005, 6002 and 6003. The gate insulatingfilm 5006 is formed of an insulating film containing silicon to have athickness of 40 to 150 nm by using plasma CVD method or sputteringmethod. In this example, as the gate insulating film 5006, a siliconoxynitride film is formed with a thickness of 110 nm by plasma CVDmethod. Of course, the gate insulating film 5006 is not limited to thesilicon oxynitride film, and another insulating film containing siliconmay be used in a single layer structure or a laminate structure.

Note that, in the case where a silicon oxide film is used as the gateinsulating film 5006, the gate insulating film may be formed such that:TEOS (tetraethyl orthosilicate) and O2 are mixed by the plasma CVDmethod; a reaction pressure of 40 Pa and a substrate temperature of 300to 400° C. are set; and an electric discharge is made with a highfrequency (13.56 MHz) power density of 0.5 to 0.8 W/cm₂. The siliconoxide film formed through the above step can obtain a satisfactorycharacteristic as the gate insulating film 5006 by subsequent thermalannealing at 400 to 500° C.

Then, over the gate insulating film 5006, a first conductive film 5007with a thickness of 20 to 100 nm and a second conductive film 5008 witha thickness of 100 to 400 nm are formed in lamination. In this example,the first conductive film 5007 comprised of a 30 nm thick TaN film andthe second conductive film 5008 comprised of a 370 nm thick W film areformed in lamination.

In this example, the TaN film as the first conductive film 5007 isformed using a Ta target in an atmosphere containing nitrogen bysputtering method. Further, the W film as the second conductive film5008 is formed using a W target by sputtering method. In addition, the Wfilm may be formed by thermal CVD method with the use of tungstenhexafluoride (WF6).

Note that the TaN film and the W film are used as the first conductivefilm 5007 and the second conductive film 5008, respectively, in thisexample, but the materials for constituting the first conductive film5007 and the second conductive film 5008 are not particularly limited.The first conductive film 5007 and the second conductive film 5008 eachmay be formed from an element selected from the group consisting of Ta,W, Ti, Mo, Al, Cu, Cr and Nd, or an alloy material or compound materialwhich contains the element as a main constituent. Further, theconductive films may be formed of a semiconductor film typified by apolycrystalline silicon film doped with an impurity element such asphosphorus or an AgPdCu alloy.

Next, a mask 5009 is formed of resist by using a photolithographymethod, and a first etching process for forming electrodes and wiringsis performed. The first etching process is performed under first andsecond etching conditions. (FIG. 3B)

In this example, as to the first etching conditions, etching isperformed by using an ICP (inductively coupled plasma) etching methodsuch that: CF₄, C₁₂ and O₂ are used as an etching gas; the gas flow rateis set to 25:25:10 sccm; and an RF (13.56 MHz) power of 500 W is appliedto a coil shape electrode under a pressure of 1.0 Pa to generate plasma.An RF (13.56 MHz) power of 150 W is also applied to the substrate side(sample stage), and a substantially negative self-bias voltage isapplied thereto. Then, the W film is etched under the first etchingconditions to form end portions of the first conductive film 5007 into atapered shape.

Subsequently, the first etching conditions are changed into the secondetching conditions without removing the mask 5009 made of resist.Etching is performed for about 15 seconds such that: CF₄ and Cl₂ areused as an etching gas; the gas flow rate is set to 30:30 sccm; and anRF (13.56 MHz) power of 500 W is applied to a coil shape electrode undera pressure of 1.0 Pa to generate plasma. An RF (13.56 MHz) power of 20 Wis also applied to the substrate side (sample stage), and asubstantially negative self-bias voltage is applied thereto. Under thesecond etching conditions, both the first conductive layer 5007 and thesecond conductive layer 5008 are etched to substantially the same level.Note that an etching time may be increased at a rate of about 10 to 20%in order to perform etching without residue on the gate insulating film5006.

In the first etching process, the mask made of resist is formed into anappropriate shape, whereby the end portions of the first conductivelayer 5007 and of the second conductive layer 5008 are formed into atapered shape due to an effect of the bias voltage applied to thesubstrate side. In this way, first shape conductive layers 5010 to 5014,6010 and 6011 that each consist of the first conductive layer 5007 andthe second conductive layer 5008 are formed by the first etchingprocess. In the gate insulating film 5006, the regions reduced inthickness are formed because the regions are not covered by the firstshape conductive layers 5010 to 5014, 6010 and 6011 and etched by about20 to 50 nm.

Next, a second etching process is performed without removing the mask5009 made of resist. (FIG. 3C) In the second etching process, etching isperformed for about 25 seconds such that: SF₆, Cl₂ and O₂ are used as anetching gas; the gas flow rate is set to 24:12:24 sccm; an RF (13.56MHz) power of 700 W is applied to the coil side under a pressure of 1.3Pa to generate plasma. An RF (13.56 MHz) power of 10 W is also appliedto the substrate side (sample stage), and a substantially negativeself-bias voltage is applied. In this way, the W film is selectivelyetched to form second shape conductive layers 5015 to 5019, 6015 and6016. At this time, first conductive layers 5015 a to 5019 a, 6015 a and6016 a are hardly etched.

Then, a first doping process is performed without removing the mask 5009made of resist to add an impurity element imparting n-type conductivityto the semiconductor layers 5002 to 5005, 6002 and 6003 at a lowconcentration. The first doping process may be conducted by an iondoping method or an ion implantation method. As to the conditions of theion doping method, doping is performed with a dosage of 1×10¹³ to 5×10¹⁴atoms/cm² and an acceleration voltage of 40 to 80 keV In this example,doping is performed with a dosage of 5.0×10¹³ atoms/cm² and anacceleration voltage of 50 keV. An element belonging to group 15 may beused as the impurity element imparting n-type conductivity. Phosphorous(P) or arsenic (As) is typically used, and phosphorus (P) is used inthis example. In this case, the second shape conductive layers 5015 to5019, 6015 and 6016 serve as masks against the impurity elementimparting n-type conductivity, and first impurity regions (n⁻ regions)5020 to 5023, 6020 and 6021 are formed in a self-aligning manner Then,the impurity element imparting n-type conductivity is added to the firstimpurity regions 5020 to 5023, 6020 and 6021 in a concentration range of1×10¹⁸ to 1×10²⁰ atoms/cm³.

Subsequently, after the mask 5009 made of resist is removed, a mask 5024made of resist is newly formed, and a second doping process is performedat an acceleration voltage higher than that in the first doping process.As to the conditions of the ion doping method, doping is performed witha dosage of 1×10¹³ to 3×10¹⁵ atoms/cm² and an acceleration voltage of 60to 120 keV. In this example, doping is performed with a dosage of3.0×10¹⁵ atoms/cm² and an acceleration voltage of 65 keV. The seconddoping process is performed using second conductive layers 5015 b to5018 b, 6015 b and 6016 b as masks against the impurity element suchthat the impurity element is added to the semiconductor layers under thetapered portions of the first conductive layers 5015 a to 5018 a, 6015 aand 6016 a. Subsequently, a third doping process is performed bylowering the acceleration voltage to obtain the state of FIG. 3D. Dosageis set to 1×10¹⁵ to 1×10¹⁷ atoms/cm³ and acceleration voltage is set to50 to 100 keV as the conditions of ion doping.

As a result of conducting the second and third doping processes, asecond impurity regions (n− region, Lov region) 5026 and 6026 whichoverlap the first conductive layer is added with the impurity elementimparting n-type conductivity in a concentration range of 1×10¹⁸ to5×10¹⁹ atoms/cm³. Also, third impurity regions (n⁺ regions) 5025, 5028and 6025 are added with the impurity element imparting n-typeconductivity in a concentration range of 1×10¹⁹ to 5×10²¹ atoms/cm³.Further, after the first and second doping processes, regions to whichno impurity element is completely added or regions to which a minuteamount of impurity element is added are formed in the semiconductorlayers 5002 to 5005, 6002 and 6003. In this example, the regions towhich no impurity element is added or the regions to which a minuteamount of impurity element is added are called channel regions 5027,5030 and 6027. Further, among the first impurity regions (n⁻ regions)5020 to 5023, 6020 and 6021 formed by the first doping process, a regionexists which is covered by the resist 5024 in the second doping process.The region is continuously called a first impurity region (n⁻ region,LDD region) 5029 in this example.

Note that the second impurity regions (n− region) 5026, 6026 and thethird impurity regions (n⁺ regions) 5025, 5028 and 6025 are formed byonly the second doping process in this example, but the presentinvention is not limited to this. The above regions may be formed byplural doping processes while appropriately changing the doping processconditions.

Then, as shown in FIG. 4A, after the mask 5024 made of resist isremoved, a mask 5031 made of resist is newly formed. Thereafter, afourth doping process is performed. Through the fourth doping process,fourth impurity regions (p⁺ regions) 5032, 5034, 6032 and fifth impurityregions (p⁻ regions) 5033, 5035, 6033, which are added with an impurityelement imparting conductivity opposite to the first conductivity, areformed into the semiconductor layers that serve as active layers ofp-channel TFTs.

In the fourth doping process, the second conductive layers 5016 b and5018 b are used as masks against the impurity element. In this way, theimpurity element imparting p-type conductivity is added to form thefourth impurity regions (p+ regions) 5032, 5034, 6032 and the fifthimpurity regions (p⁻ regions) 5033, 5035, and 6033 in a self-aligningmanner.

In this example, the fourth impurity regions 5032, 5034, 6032 and thefifth impurity regions 5033, 5035, 6033 are formed by an ion dopingmethod using diborane (B₂H₆). As the conditions of the ion dopingmethod, a dosage of 1×10¹⁶ atoms/cm² and an acceleration voltage of 80keV are adopted.

Note that the semiconductor layers for forming n-channel TFTs arecovered with the mask 5031 made of resist in the fourth doping process.

Here, by the first and second doping processes, the fourth impurityregions (p⁺ regions) 5032, 5034, 6032 and the fifth impurity regions (p⁻regions) 5033, 5035, 6033 have been added with phosphorus at differentconcentrations. However, any of the fourth impurity regions (p⁺ regions)5032, 5034, 6032 and the fifth impurity regions (p⁻ regions) 5033, 5035,6033 is subjected to the fourth doping process such that theconcentration of the impurity element imparting p-type conductivity is1×10¹⁹ to 5×10²¹ atoms/cm³. Thus, the fourth impurity regions (p⁺regions) 5032, 5034, 6032 and the fifth impurity regions (p⁻ regions)5033, 5035, 6033 function as source regions and drain regions of thep-channel TFTs without problems.

Note that the fourth impurity regions (p⁺ regions) 5032, 5034, 6032 andthe fifth impurity regions (p⁻ regions) 5033, 5035, 6033 are formed byonly the fourth doping process in this example, but the presentinvention is not limited to this. The above regions may be formed byplural doping processes while appropriately changing the doping processconditions.

Then, as shown in FIG. 4B, the mask 5031 made of resist is removed, andthen, a first interlayer insulating film 5036 is formed. As the firstinterlayer insulating film 5036, an insulating film containing siliconis formed to have a thickness of 100 to 200 nm by using plasma CVDmethod or sputtering method. In this example, a silicon oxynitride filmwith a thickness of 100 nm is formed by plasma CVD method. Of course,the first interlayer insulating film 5036 is not limited to the siliconoxynitride film, and another insulating film containing silicon may beused in a single layer or laminate structure.

Then, as shown in FIG. 4C, heat treatment (thermal treatment) isconducted to recover the crystallinity of the semiconductor layers andactivate the impurity elements added to the semiconductor layers. Theheat treatment is conducted by a thermal annealing method using furnaceannealing. The thermal annealing method is preferably conducted in anitrogen atmosphere at an oxygen concentration of 1 ppm or less,preferably 0.1 ppm or less at 400 to 700° C. In this example, theactivation process is performed by thermal treatment at 410° C. for 1hour. Note that, in addition to the thermal annealing method, a laserannealing method or a rapid thermal annealing method (RTA method) may beapplied.

Further, heat treatment may be performed before the formation of thefirst interlayer insulating film 5036. Incidentally, in the case wherethe materials that constitute the first conductive layers 5015 a to 5019a, 6015 a and 6015 b and the second conductive layers 5015 b to 5019 b,6015 b and 6016 b are easily affected by heat, it is preferable thatheat treatment is conducted after the first interlayer insulating film5036 (insulating film containing silicon as a main constituent, forexample, silicon nitride film) is formed in order to protect wirings andthe like, as in this example.

Heat treatment is conducted after the formation of the first interlayerinsulating film 5036 (insulating film containing silicon as a mainconstituent, for example, silicon nitride film) as described above,whereby hydrogenation of the semiconductor layers can be performedsimultaneously with the activation process. In the hydrogenation step,dangling bonds of the semiconductor layers are terminated by hydrogencontained in the first interlayer insulating film 5036.

Note that heat treatment for hydrogenation may be performed in additionto the heat treatment for the activation process.

Here, the semiconductor layers can be hydrogenated irrespective of theexistence of the first interlayer insulating film 5036. As another meansfor hydrogenation, there may be used means with the use of hydrogenexcited by plasma (plasma hydrogenation) or means of conducting heattreatment at 300 to 450° C. for 1 to 12 hours in an atmospherecontaining 3 to 100% of hydrogen.

Next, a second interlayer insulating film 5037 is formed over the firstinterlayer insulating film 5036. An inorganic insulating film may beused as the second interlayer insulating film 5037. For example, asilicon oxide film formed by a CVD method, a silicon oxide film appliedby an SOG (spin on glass) method, or the like may be used. In addition,as the second interlayer insulating film 5037, an organic insulatingfilm may be used. For example, a film made of polyimide, polyamide, BCB(benzocyclobutene), acrylic, or the like may be used. Further, alaminate structure of an acrylic film and a silicon oxynitride film mayalso be used.

In this example, an acrylic film with a thickness of 1.6 μm is formed.The second interlayer insulating film 5037 can reduce unevenness due tothe TFTs formed over the substrate 5000 and provide levelness.Particularly, the second interlayer insulating film 5037 is providedmainly for attaining levelness, and thus is preferably a film excellentin levelness.

Next, the second interlayer insulating film 5037, the first interlayerinsulating film 5036, and the gate insulating film 5006 are etched byusing dry etching or wet etching, thereby forming contact holes thatreach the third impurity regions 5025, 5028, 6025 and the fourthimpurity regions 5032, 5034, 6032.

Subsequently, wirings 5038 to 5041, 6038, 6039 and a pixel electrode5042, which are electrically connected with the respective impurityregions, are formed. Note that these wirings are formed by patterning alaminate film consisting of a 50 nm thick Ti film and a 500 nm thickalloy film (alloy film of Al and Ti). Of course, the present inventionis not limited to a two-layer structure, and a single layer structure ora laminate structure of three or more layers may be adopted. Further,the materials for wirings are not limited to Al and Ti. For example, thewirings may be formed by patterning a laminate film in which an Al filmor a Cu film is formed on a TaN film, and a Ti film is further formedthereon. In any case, a material excellent in reflecting property isdesirably used.

Thereafter, an orientation film 5043 is formed over a portion at leastcontaining the pixel electrode 5042, and a rubbing process is performedthereto. Note that, in this example, a columnar spacer 5045 formaintaining a substrate interval is formed at a desired position bypatterning an organic resin film such as an acrylic resin film beforethe orientation film 5043 is formed. Further, a spherical spacer may bescattered over the surface of the substrate instead of the columnarspacer.

Next, a counter substrate 5046 is prepared. Colored layers (colorfilters) 5047 to 5049 and a leveling film 5050 are formed over thecounter substrate 5046. At this time, the first colored layer 5047 andthe second colored layer 5048 are overlapped to form a light shieldingportion. Further, the first colored layer 5047 and the third coloredlayer 5049 may be partially overlapped to form a light shieldingportion. Alternatively, the second colored layer 5048 and the thirdcolored layer 5049 may be partially overlapped to form a light shieldingportion.

In this way, a gap between pixels is shielded against light by the lightshielding portion comprised of a lamination layer of the colored layerswithout newly forming a light shielding portion. Thus, the number ofsteps can be reduced.

Then, a counter electrode 5051 comprised of a transparent conductivefilm is formed at least over a portion, which corresponds to a pixelportion, of the leveling film 5050, and an orientation film 5052 isformed over the substrate of the counter substrate. Then, a rubbingprocess is performed thereto.

Then, the active matrix substrate over which the pixel portion and thedriver circuit are formed and the counter substrate are bonded to eachother by a sealing material 5044. The sealing material 5044 is mixedwith a filler, and the two substrates are bonded while a uniforminterval is kept by the filler and the columnar spacer. Thereafter, aliquid crystal material 5053 is injected between both the substrates,and complete sealing is conducted with a sealant (not shown). A knownliquid crystal material may be used as the liquid crystal material 5053.Thus, the liquid crystal display device shown in FIG. 4D is completed.Then, if necessary, the active matrix substrate or the counter substrateis cut into a desired shape. Further, a polarizing plate and an FPC (notshown) are bonded to the liquid crystal display device.

As described above, regions that require high-speed operation andregions to the contrary thereof, by varying the process of semiconductorfilm activation, a semiconductor device with high-speed operation in itsentirety can be manufactured through a high throughput manufacturingprocess.

In particular, in the first region (a region having a circuit block thatrequires high-speed operation), the TFT having a semiconductor film inwhich large crystal grains are formed by performing the crystallizationusing wave oscillation laser is formed, thereby realizing a circuitblock with high-speed operation.

In addition, the TFT manufactured in this example may be either a bottomgate structure or a dual gate structure.

EXAMPLE 7

In Example 7, steps for manufacturing a substrate over which a circuitblock constituted of a thin film transistor and an EL display portionare integrated are described.

Note that, the steps up to the step shown in FIG. 5A are similar tothose shown in FIGS. 3A to 3D and 4A in Example 6.

Portions similar to FIGS. 3A to 3D and 4A to 4D are indicated using thesame symbols and the description is omitted here.

As shown in FIG. 5A, a first interlayer insulating film 5101 is formed.An insulating film containing silicon is formed as the first interlayerinsulating film 5101 at a thickness of 100 nm to 200 nm by plasma CVDmethod or sputtering method. In this example, a silicon oxynitride filmhaving a film thickness of 100 nm is formed by plasma CVD method. Ofcourse, the first interlayer insulating film 5101 is not limited to thesilicon oxynitride film, and therefore another insulating filmcontaining silicon may be used as a single layer or a laminatestructure.

Next, as shown in FIG. 5B, heat treatment (thermal processing) isperformed for the recovery of crystallinity of the semiconductor layersand the activation of the impurity element added to the semiconductorlayers. This heat treatment is performed by a thermal anneal methodusing a furnace anneal furnace. The thermal anneal method is preferablyconducted in a nitrogen atmosphere in which an oxygen concentration is 1ppm or less, preferably, 0.1 ppm or less at 400° C. to 700° C. In thisexample, the heat treatment at 410° C. for 1 hour is performed for theactivation processing. However, if a laser anneal method or a rapidthermal anneal method (RTA method) can be applied in addition to thethermal anneal method.

Also, the heat treatment may be performed before the formation of thefirst interlayer insulating film 5101. Note that, the first conductivelayers 5015 a to 5019 a and the second conductive layers 5015 b to 5019b are sensitive to heat, it is preferable that heat treatment isperformed after the first interlayer insulating film 5101 (insulatingfilm containing mainly silicon, for example, silicon nitride film) forprotecting a wiring and the like is formed as in this example.

As described above, when the heat treatment is performed after theformation of the first interlayer insulating film 5101 (insulating filmcontaining mainly silicon, for example, silicon nitride film), thehydrogenation of the semiconductor layer can be also conductedsimultaneously with the activation processing. In the hydrogenationstep, a dangling bond of the semiconductor layer is terminated byhydrogen contained in the first interlayer insulating film 5101.

Note that heat treatment for hydrogenation other than the heat treatmentfor activation processing may be performed.

Here, the semiconductor layer can be hydrogenated regardless of thepresence or absence of the first interlayer insulating film 5101. Asanother means for hydrogenation, means for using hydrogen excited byplasma (plasma hydrogenation) or means for performing heat treatment inan atmosphere containing hydrogen of 3% to 100% at 300° C. to 450° C.for 1 hour to 12 hours may be used.

By the above steps, the CMOS circuit composed of the N-channel TFT andthe P-channel TFT can be formed in the pixel portion.

Next, a second interlayer insulating film 5102 is formed on the firstinterlayer insulating film 5101. An inorganic insulating film can beused as the second interlayer insulating film 5102. For example, asilicon oxide film formed by CVD method, a silicon oxide film applied bySOG (spin on glass) method, or the like can be used. In addition, anorganic insulating film can be used as the second interlayer insulatingfilm 5102. For example, a film made of polyimide, polyamide, BCB(benzocyclobutene), acrylic, or the like can be used. Further, alaminate structure of an acrylic film and a silicon oxide film may beused. Further more, a laminate structure of an acrylic film and asilicon nitride film or a silicon oxynitride film formed by sputteringmethod also may be used.

Next, using dry etching or wet etching, the first interlayer insulatingfilm 5101, the second interlayer insulating film 5102, and the gateinsulating film 5006 are etched to form contact holes which reachimpurity regions (third impurity regions (N+ regions) and fourthimpurity regions (P+ regions)) of respective TFTs which compose thecircuit block.

Next, wirings 5103 to 5109, 6103 and 6104 electrically connected withthe respective impurity regions are formed. Note that, in this example,a Ti film having a film thickness of 100 nm, an Al film having a filmthickness of 350 nm, and a Ti film having a film thickness of 100 nm areformed in succession by a sputtering method and a resultant laminatefilm is patterned in a predetermined shape so that the wirings 5103 to5109, 6103 and 6104 are formed.

Of course, they are not limited to a three-layer structure. A singlelayer structure, a two-layer structure, or a laminate structure composedof four layers or more may be used. Materials of the wirings are notlimited to Al and Ti, and therefore other conductive films may be used.For example, it is preferable that an Al film or a Cu film is formed ona TaN film, a Ti film is formed thereon, and then a resultant laminatefilm is patterned to form the wirings.

Next, as shown in FIG. 5C, a third interlayer insulating film 5110 isformed. An inorganic insulating film or an organic insulating film canbe used as the third interlayer insulating film 5110. A silicon oxidefilm formed by a CVD method, a silicon oxide film applied by an SOG(spin on glass) method, or the like can be used as the inorganicinsulating film. In addition, an acrylic resin film or the like can beused as the organic insulating film. Further, a laminate structure of anacrylic film and a silicon nitride film or a silicon oxynitride film maybe used.

When the third interlayer insulating film 5110 is formed, unevennesscaused by TFTs formed over the substrate 5000 is reduced and the surfacecan be leveled. In articular, the third interlayer insulating film 5110is for leveling. Thus, a film having superior evenness is preferable.

Next, using dry etching or wet etching, the third interlayer insulatingfilm 5110 is etched to form contact holes which reach the wiring 5108.

Next, a conductive film is patterned to form a pixel electrode 5111. Inthe case of this example, an alloy film of aluminum and lithium is usedas the conductive film. Of course, a known MgAg film (alloy film ofmagnesium and silver) may be used. The pixel electrode 5111 correspondsto the cathode of the EL element. A conductive film made of an elementwhich belongs to Group 1 or Group 2 of the periodic table or aconductive film to which those elements are added can be freely used asa cathode material.

The pixel electrode 5111 is electrically connected with the wiring 5108through a contact hole formed in the third interlayer insulating film5110. Thus, the pixel electrode 5111 is electrically connected with oneof the source region and the drain region comprising the drive circuit.

Next, as shown in FIG. 5D, banks 5112 are formed such that EL layers ofrespective pixels are separated from each other. The banks 5112 areformed from an inorganic insulating film or an organic insulating film.A silicon nitride film or a silicon oxynitride film formed by asputtering method, a silicon oxide film formed by a CVD method, asilicon oxide film applied by an SOG method, or the like can be used asthe inorganic insulating film. In addition, an acrylic resin film or thelike can be used as the organic insulating film.

Here, when a wet etching method is used at the formation of the banks5112, they can be easily formed as side walls having taper shapes. Ifthe side walls of the banks 5112 are not sufficiently gentle, thedeterioration of an EL layer caused by a step becomes a marked problem.Thus, attention is required.

Examples of a combination of the third interlayer insulating film 5110and the banks 5112 will be described below.

There is a combination in which a laminate film of an acrylic and asilicon nitride film or a silicon oxynitride film formed by a sputteringmethod is used as the third interlayer insulting film 5110, while asilicon nitride film or a silicon oxynitride film formed by a sputteringmethod is used as the banks 5112. In addition, there is a combination inwhich a silicon oxide film formed by a plasma CVD method is used as thethird interlayer insulating film 5110 and a silicon oxide film formed bya plasma CVD method is used as the banks 5112. In addition, there is acombination in which a silicon oxide film formed by an SOG method isused as the third interlayer insulating film 5110 and a silicon oxidefilm formed by an SOG method is used as the banks 5112. In addition,there is a combination in which a laminate film of a silicon oxide filmformed by an SOG method and a silicon oxide film formed by a plasma CVDmethod is used as the third interlayer insulating film 5110 and asilicon oxide film formed by a plasma CVD method is used as the banks5112. In addition, there is a combination in which acrylic is used forthe third interlayer insulating film 5110 and acrylic is used for thebanks 5112. In addition, there is a combination in which a laminate filmof an acrylic film and a silicon oxide film formed by a plasma CVDmethod is used as the third interlayer insulating film 5110 and asilicon oxide film formed by a plasma CVD method is used as the banks5112. In addition, there is a combination in which a silicon oxide filmformed by a plasma CVD method is used as the third interlayer insulatingfilm 5110 and acrylic is used for the banks 5112.

A carbon particle or a metallic particle may be added into the banks5112 to reduce resistivity, thereby suppressing the generation of staticelectricity. At this time, the amount of carbon particle or metallicparticle to be added is preferably adjusted such that the resistivitybecomes 1×10⁶ Ωm to 1×10¹² Ωm (preferably, 1×10⁸ Ωm to 1×10¹⁰ Ωm).

Next, an EL layer 5113 is formed on the pixel electrode 5038 which issurrounded by the banks 5112 and exposed.

An organic light emitting material or an inorganic light emittingmaterial which is known can be used as the EL layer 5113.

A low molecular weight based organic light emitting material, a highmolecular weight based organic light emitting material, or anintermediate molecular weight based organic light emitting material canbe freely used as the organic light emitting material. Note that in thisspecification, an intermediate molecular weight based organic lightemitting material indicates an aggregate of an organic compound whichhas no subliming property or dissolving property (preferably, anaggregate which has molecularity of 10 μm or less).

The EL layer 5113 has generally a laminate structure. Typically, thereis a laminate structure of “a hole transporting layer, a light emittinglayer, and an electron transporting layer”, which has been proposed byTang et al. in Eastman Kodak Company. In addition to this, a structurein which “an electron transporting layer, a light emitting layer, a holetransporting layer, and an hole injection layer” or “an electroninjection layer, a light emitting layer, an hole transporting layer, anda hole injection layer” are laminated on an cathode in this order may beused. A light emitting layer may be doped with fluorescent pigment orthe like. However, the electric charge excitation before emitting lightmay be triplet or singlet.

In this specification, a light emitting element can utilize eitherphosphorescence from triplet excitation to ground state or fluorescenceemission from singlet excitation to ground state.

In this example, the EL layer 5113 is formed by an evaporation methodusing a low molecular weight based organic light emitting material.Specifically, a laminate structure in which a tris-8-quinolinolatoaluminum complex (Alq₃) film having a thickness of 70 nm is provided asthe light emitting layer and a copper phthalocyanine (CuPc) film havinga thickness of 20 nm is provided thereon as the light emitting layer isused. A light emission color can be controlled by adding fluorescentpigment such as quinacridon, perylene, or DCM1 to Alq₃.

Note that only one pixel is shown in FIG. 5D. However, a structure inwhich the EL layer 5113 corresponding to respective colors of, pluralcolors, for example, R (red), G (green), and B (blue) are separatelyformed can be used.

Also, as an example using the high molecular weight based organic lightemitting material, the EL layer 5113 may be constructed by a laminatestructure in which a polythiophene (PEDOT) film having a thickness of 20nm is provided as the hole injection layer by a spin coating method anda paraphenylenevinylene (PPV) film having a thickness of about 100 nm isprovided thereon as the light emitting layer. When π conjugated systempolymer of PPV and a derivative of PPV are used, a light emissionwavelength from red to blue can be selected. In addition, an inorganicmaterial such as silicon carbide can be used for the electrontransporting layer and the electron injection layer.

Note that the EL layer 5113 is not limited to a layer having a laminatestructure in which the hole injection layer, the hole transportinglayer, the light emitting layer, the electron transporting layer, theelectron injection layer, and the like are distinct. In other words, theEL layer 5113 may have a laminate structure with a layer in whichmaterials composing the hole injection layer, the hole transportinglayer, the light emitting layer, the electron transporting layer, theelectron injection layer, and the like are mixed.

For example, the EL layer 5113 may have a structure in which a mixedlayer composed of a material composing the electron transporting layer(hereinafter referred to as an electron transporting material) and amaterial composing the light emitting layer (hereinafter referred to asa light emitting material) is located between the electron transportinglayer and the light emitting layer.

Next, a pixel electrode 5114 made from a transparent conductive film isformed on the EL layer 5113. A compound of indium oxide and tin oxide(ITO), a compound of indium oxide and zinc oxide, zinc oxide, tin oxide,indium oxide, or the like can be used for the transparent conductivefilm. In addition, the transparent conductive film to which gallium isadded may be used. The pixel electrode 5114 corresponds to the anode ofthe EL element.

When the pixel electrode 5114 is formed, the EL element is completed.Note that the EL element indicates a diode composed of the pixelelectrode (cathode) 5111, the EL layer 5113, and the pixel electrode(anode) 5114.

It is effective that a protective film (passivation film) 5115 isprovided to completely cover the EL element. A single layer of aninsulating film such as a carbon film, a silicon nitride film, or asilicon oxynitride film, or a laminate layer of a combination thereofcan be used as the protective film 5115.

Note that, when light emitted from the EL element is radiated from thepixel electrode 5114 side as in this example, it is necessary to use afilm which transmits light as a protective film 5115.

Note that it is effective that steps up to the formation of theprotective film 5115 after the formation of the banks 5112 are conductedin succession using a multi-chamber type (or in-line type) filmformation apparatus without being exposed to air.

Note that, actually, when it is completed up to the state shown in FIG.5D, in order not to be exposed to air, it is preferable that packaging(sealing) is conducted using a protective film (laminate film,ultraviolet curable resin film, or the like) or a sealing member whichhas a high airtight property and low degassing. At the same time, whenan inner portion surrounded by the sealing member is made to an inertatmosphere or a hygroscopic material (for example, barium oxide) islocated in the inner portion, the reliability of the EL element isimproved.

Also, after an airtightness level is improved by processing such aspackaging, a connector (flexible printed circuit: FPC) for connectingterminals led from elements or circuits which are formed over thesubstrate 5000 with external signal terminals is attached so that it iscompleted as a product.

Additionally, the TFT manufactured in this example can be a structure ofbottom gate or dual gate having two gate electrodes arranged in the upand down of channel region through an insulating film therebetween.

EXAMPLE 8

One example of a semiconductor device of the invention is described inthis Example with reference to FIG. 16.

In FIG. 16, the semiconductor device is constituted by a pixel region1600, a scanning line drive circuit 1601, a signal line drive circuit1602, a VRAM 1603, a CPU 1604, a memory 1605 and an interface circuit1606, which are formed integrally over a substrate having an insulatingsurface.

Described below is the operation of the semiconductor device shown inFIG. 16. The image data and the control signal of an external unit arecommunicated between the CPU 1604 and the external unit through theinterface circuit 1606 and a system bus 1607. A keyboard, a ROM and thelike can be exemplified as external units. The CPU 1604 temporarilystores the image data being processed and the control signal of thelogic circuit in the memory 1605, and the processed image data arestored in the VRAM 1603. The image data stored in the VRAM 1603 aredisplayed on the pixel region 1600 due to the signal line drive circuit1602 and scanning line drive circuit 1601.

The VRAM is a memory for storing the image data, and is constituted by avolatile memory such as SRAM or DRAM. A volatile memory such as SRAM orDRAM is also used as the memory 1605. The interface circuit works totemporarily store the signals input from the external unit, to convertthe signals into a format that can be used in the circuit, and executesother control operations.

In this Example, the circuit blocks included in the region 1 must beoperated at a particularly high speed. As described in Examples 3 to 6,therefore, there is applied a process for fabricating high-mobility TFTsby using a step of crystallizing the semiconductor film with thecontinuous wave laser.

By applying the process for fabricating high-mobility TFTs to the region1, the circuit blocks included in the region 1 operate at a high speed.

When the SRAM is used as the memory, a reading cycle of 200 nsec isrealized and when the DRAM is used as the memory, a reading cycle ofshorter than 1 μsec is realized.

Further, the CPU having an operation frequency of not lower than 5 MHzis realized.

In this Example, the process for fabricating high-mobility TFTs wasapplied to the region 1. The invention, however, is not limited thereto.The person who conducts the process may apply the process forfabricating high-mobility TFTs to any region depending upon the use ofthe semiconductor device.

In this case, it is desired that the areas to which the process forfabricating high-mobility TFTs is applied are not larger than 50%(preferably not larger than 30%) of the whole areas of the substrate1608. It is further desired that the regions 1 exist in a number assmall as possible (preferably not larger than 10) and have a rectangularshape.

This Example can be used in combination with Examples 1 to 7.

EXAMPLE 9

One example of a semiconductor device of the invention is described inthis Example with reference to FIG. 17.

In FIG. 17, the semiconductor device is constituted by a pixel region1700, a scanning line drive circuit 1701, a signal line drive circuit1702, a frame memory 1703, a timing-forming circuit 1705 and a formatconversion unit 1704, which are formed integrally over a substratehaving an insulating surface.

The constitution of this Example will now be described.

The timing-forming circuit 1705 forms clock signals for determiningoperation timings of the scanning line drive circuit 1701 and the signalline drive circuit 1702. The format conversion unit 1704 expands anddecodes compressed and encoded signals inputted from the external unitthrough the FPC 1706 and conducts the image processing such asinterpolation and resizing. The image data subjected to the formatconversion are stored in the frame memory 1703. The image data stored inthe frame memory 1703 are displayed on the pixel region 1700 due to thescanning line drive circuit 1701 and the signal line drive circuit 1702.

In this embodiment, the circuit blocks included in the regions 1 mustoperate at high speeds. Therefore, there is applied the process forfabricating high-mobility TFTs using the step of crystallizing thesemiconductor film based on the continuously wave laser as described inExamples 3 to 6.

When the SRAM is used as the frame memory, a reading cycle of 200 nsecis realized and when the DRAM is used as the memory, a reading cycle ofshorter than 1 μsec is realized.

In this Example, the drive frequency of the logic circuit included inthe region 1 is not lower than 5 MHz.

In this Example, the process for fabricating high-mobility TFTs wasapplied to the regions 1. The invention, however, is not limitedthereto. The person who conducts the process may apply the process forfabricating high-mobility TFTs to any region depending upon the use ofthe semiconductor device.

In this case, it is desired that the areas to which the process forfabricating high-mobility TFTs is applied are not larger than 50%(preferably not larger than 30%) of the whole areas of the substrate1608. It is further desired that the regions 2 exist in a number assmall as possible (preferably not larger than 10) and have a rectangularshape.

This Example can be used in combination with Examples 1 to 7.

EXAMPLE 10

One Example of a semiconductor device of the invention is described inthis Example with reference to FIG. 18.

In FIG. 18, the semiconductor device is constituted by a pixel region1800, a scanning line drive circuit 1801, a signal line drive circuit1802, a VRAM 1803, a mask ROM 1804, an arithmetic processing circuit1805, an image processing circuit 1806, a memory 1807 and an interfacecircuit 1808, which are formed integrally over a substrate having aninsulating surface.

The constitution of this Example will now be described.

Control signals are communicated with the external unit through theinterface circuit 1808 and the system bus 1809. A keyboard or the likecan be exemplified as the external unit. Program data and image data arestarted in the mask ROM 1804. The data stored in the mask ROM areprocessed while being read and written to and from the memory 1807 atall times by the arithmetic processing circuit 1805. The image data areprocessed such as resized through the image processing circuit 1806 andare stored in the VRAM 1803. The data stored in the VRAM 1803 aredisplayed on the pixel region 1800 due to the scanning line drivecircuit 1801 and the signal line drive circuit 1802.

SRAM and DRAM are used as the memories and VRAMs.

In this embodiment, the image processing circuit operates at a frequencyof not lower than 5 MHz. Further, the CPU operates at a frequency of notlower than 5 MHz.

In this Example, the circuit blocks included in the regions 1 must beoperated at a particularly high speed. As described in Examples 3 to 6,therefore, there is applied a process for fabricating high-mobility TFTsby using a step of crystallizing the semiconductor film with thecontinuous wave laser.

In this Example, the process for fabricating high-mobility TFTs wasapplied to the regions 1. The invention, however, is not limitedthereto. The person who conducts the process may apply the process forfabricating high-mobility TFTs to any region depending upon the use ofthe semiconductor device.

In this case, it is desired that the areas to which the process forfabricating high-mobility TFTs is applied are not larger than 50%(preferably not larger than 30%) of the whole areas of the substrate1608. It is further desired that the regions 2 exist in a number assmall as possible (preferably not larger than 10) and have a rectangularshape.

This Example can be used in combination with Examples 1 to 7.

EXAMPLE 11

Examples of electronic devices to which the present invention is appliedinclude a video camera, a digital camera, a goggle type display(head-mounted display), a navigation system, a sound reproducing system(car audio system, audio component stereo, or the like), a notebookpersonal computer, a game player, a portable information terminal(mobile computer, portable telephone, portable game player, electronicbook, or the like), and an image reproducing system provided with arecording medium (specifically, device which plays a recording mediumsuch as a digital versatile disc (DVD) and is provided with a displayfor displaying images). Specific examples of the electronic devices areshown in FIGS. 19A to 19G.

FIG. 19A shows a display device, which includes a casing 1401, a supportstand 1402, and a display portion 1403. The present invention can beapplied to the display portion 1403.

FIG. 19B shows a video camera, which is constituted by a main body 1411,a display portion 1412, a sound input portion 1413, operation switches1414, a battery 1415, an image receiving portion 1416, and the like. Thepresent invention can be applied to the display portion 1412.

FIG. 19C shows a notebook personal computer, which is constituted by amain body 1421, a casing 1422, a display portion 1423, a keyboard 1424,and the like. The present invention can be applied to the displayportion 1423.

FIG. 19D shows a portable information terminal, which is constituted bya main body 1431, a stylus 1432, a display portion 1433, operationbuttons 1434, an external interface 1435, and the like. The presentinvention can be applied to the display portion 1433.

FIG. 19E shows a sound reproducing system, specifically, an audio systemfor an automobile, which is constituted by a main body 1441, a displayportion 1442, operation switches 1443 and 1444, and the like. Thepresent invention can be applied to the display portion 1442. Further,the audio system for an automobile is taken as an example here, but aportable or domestic audio system may be given.

FIG. 19F shows a digital camera, which is constituted by a main body1451, a display portion A 1452, an eyepiece portion 1453, operationswitches 1454, a display portion B 1455, a battery 1456, and the like.The present invention can be applied to the display portion A 1452 andthe display portion B 1455.

FIG. 19G shows a portable telephone, which is constituted by a main body1461, a sound output portion 1462, a sound input portion 1463, a displayportion 1464, operation switches 1465, an antenna 1466, and the like.The present invention can be applied to the display portion 1464.

Not only a glass substrate but also a heat-resistance plastic substratecan be used for the display device used in each of the above electronicdevices. Thus, reduction in weight of the electronic device can beattained.

Note that examples shown in Example 11 are no more than some applicationexamples. It should be mentioned that the present invention is notlimited to these uses.

Example 11 can be performed by freely combining with Embodiments andExamples 1 to 7.

In this invention, the semiconductor display unit and other circuitblocks are integrally formed over the substrate having an insulatingsurface by employing the process for fabricating TFTs that realize ahigh degree of mobility. As the process for fabricating TFTs forrealizing a high degree of mobility, there is employed a step ofcrystallizing the semiconductor active layer by employing the continuouswave laser.

Accordingly, there are provided a small semiconductor device having adisplay unit featuring improved reliability by mounting IC chips overthe substrate, and a semiconductor device realizing a high operationfrequency as a result of decreasing the wiring capacity by integrallyforming the IC chips and as a result of improving circuitcharacteristics.

According to this invention, further, the process for crystallizationbased on the continuous wave laser is selectively effected for onlycircuit blocks that must be operated at high speeds. This makes itpossible to greatly improve the throughput in the step ofcrystallization without decreasing the operation speed of thesemiconductor device. Owing to a great reduction in the areas of thesubstrate for mounting the IC chips and owing to a high throughput,further, there is provided a semiconductor device having a display unitat a low cost.

1. A semiconductor device comprising: a scanning line drive circuit; asignal line drive circuit, wherein at least one of the scanning linedrive circuit or the signal line drive circuit comprises a first thinfilm transistor; and a pixel region comprising a second thin filmtransistor; wherein the pixel region, the scanning line drive circuit,and the signal line drive circuit are provided on a same substrate,wherein the first thin film transistor comprises a first active layer,and the first active layer is formed by a polycrystalline semiconductorin which crystalline grains are extending in the channel direction, andwherein the second thin film transistor comprises a second active layer,and the second active layer is formed by a polycrystalline semiconductorin which shape of polycrystalline grains have an anisotropy in thechannel direction which is weaker than that of the first active layer.2. A semiconductor device according to claim 1, wherein the drivefrequency of the scanning line drive circuit is from 1 kHz to 1 MHz, andthe drive frequency of the signal line drive circuit is from 100 kHz to100 MHz.
 3. A semiconductor device according to claim 1, wherein thefirst thin film transistor is included in any one of the groupconsisting of a memory, a CPU, an image processing circuit, a DSP and atiming generating circuit, which is provided on the same substrate.
 4. Asemiconductor device according to claim 3, wherein the memory is an SRAMhaving a read cycle time of not longer than 200 nsec.
 5. A semiconductordevice according to claim 3, wherein the memory is a DRAM having a readcycle time of not longer than 1 μsec.
 6. A semiconductor deviceaccording to claim 3, wherein the operation frequency of the CPU is notlower than 5 MHz.
 7. A semiconductor device according to claim 3,wherein the operation frequency of the image processing circuit is notlower than 5 MHz.
 8. A semiconductor device according to claim 3,wherein the operation frequency of the DSP is not lower than 5 MHz.
 9. Asemiconductor device according to claim 1, wherein the substrate is anyone of a plastic substrate, a glass substrate or a quartz substrate. 10.A semiconductor device according to claim 1, wherein the area of thecircuits comprising the first thin film transistor is not larger than50% of the area of the substrate.
 11. A semiconductor device accordingto claim 1, wherein the semiconductor device is a liquid crystal displaydevice.
 12. A semiconductor device according to claim 1, wherein thesemiconductor device is a light-emitting device.
 13. An electronicdevice comprising a semiconductor device according to claim 1, whereinthe electronic device is any one selected from the group consisting of agame device, a video camera, a head-mounted type display, a DVD player,a personal computer, a cell phone and a car audio device.
 14. Asemiconductor device comprising: a scanning line drive circuit; a signalline drive circuit, wherein at least one of the scanning line drivecircuit or the signal line drive circuit comprises a first thin filmtransistor; and a pixel region comprising a second thin film transistor;wherein the pixel region, the scanning line drive circuit, and thesignal line drive circuit are provided on a same substrate, wherein thefirst thin film transistor comprises a first active layer, and the firstactive layer is formed by a polycrystalline semiconductor, and whereinthe second thin film transistor comprises a second active layer, and thesecond active layer is formed by a polycrystalline semiconductor inwhich shape of polycrystalline grains have an anisotropy in the channeldirection which is weaker than that of the first active layer.
 15. Asemiconductor device comprising: a scanning line drive circuit; a signalline drive circuit, wherein at least one of the scanning line drivecircuit or the signal line drive circuit comprises a first thin filmtransistor; and a pixel region comprising a second thin film transistor;wherein the pixel region, the scanning line drive circuit, and thesignal line drive circuit are provided on a same substrate, wherein thefirst film transistor comprises a first active layer formed by apolycrystalline semiconductor having an electric anisotropy in thechannel direction, and wherein the second thin film transistor comprisesa second active layer, and the second active layer is formed by apolycrystalline semiconductor in which shape of polycrystalline grainshave an anisotropy in the channel direction which is weaker than that ofthe first active layer.
 16. A semiconductor device comprising: ascanning line drive circuit; a signal line drive circuit, wherein atleast one of the scanning line drive circuit or the signal line drivecircuit comprises a first thin film transistor; and a pixel regioncomprising a second thin film transistor; wherein the pixel region, thescanning line drive circuit, and the signal line drive circuit areprovided on a same substrate, wherein the first thin film transistorcomprises a first active layer formed by a polycrystalline semiconductorin which polycrystalline grains are extending in the channel direction,and having a grain size of from 0.5 to 100 μm in the direction of shortdiameter thereof and a grain size of from 3 to 10,000 μm in thedirection of long diameter thereof, and wherein the second thin filmtransistor comprises a second active layer, and the second active layeris formed by a polycrystalline semiconductor in which shape ofpolycrystalline grains have an anisotropy in the channel direction whichis weaker than that of the first active layer.